Gemstones of Tanzania by Gilay Shamika
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Transcript of Gemstones of Tanzania by Gilay Shamika
2013 Sharing With Community
Gemstones of Tanzania Identification Brochure
Color, Transparency, Refractive Index, Specific Gravity, Spectrum, Inclusions and Rough Shape
Eng. Gilay Shamika
2013 Sharing With Community
PREFACE
emstones have little attention in Tanzania compared to precious metals.
Precious metals especially gold, copper and silver are known to most of
Tanzanians and the business of the same is booming on daily basis. For
gemstones is different story. Few Tanzanians who know about gemstones. When you
talk about gemstones, few people will refer to Tanzanite, Ruby and garnets only. But
there are more types of gems in Tanzania.
This compilation is aimed to provide knowledge of gemstones which are cheaply
available in abundant compared to precious metals. On top of that, they also
command higher price than gold. The knowledge also will help Tanzanians to venture
into gemstones and hence diversification of minerals business. Rather than everybody
thinking of precious metals, Tanzanians can now start thinking of gemstones.
Tanzania is believed to be the second country with higher amount of gemstones
reserves after Madagascar. Gemstones are available in alluvial form along the river
banks, swamps, and natural dams and in the valleys where the gemstones are washed
out from the mountains by rainfall drains. Umber valley in Tanga is among the famous
valleys with alluvial gemstones. The compilation has shown the areas with gemstone
reserves. This will help if somebody has found the gems at a certain area, he/she can
refer to this compilation and see what kind of gemstones are found in that .Whenever
you see any colored stone within your vicinity, think about gemstones and not just
gravels or pebbles. Consult this compilation or any Minerals office for identification.
You might be playing with a gem worth a millions of dollars!
Talk to your children and ask them to fetch any colored stone along the river banks,
swamps and dams during their normal bathing games. The adults during grazing and
farming they may see such kind of stones. It is not a joke; the records show even
Dr.Williamsons found diamonds from indigenous who were blind about diamond. The
first diamond also at south Africa Kimberly, was found within the hand of child
playing with it as a normal pebble stone and one geologist saw it and the story
changes.Songea sapphire and Tunduru Alexandrite were discovered by missionaries.
The people thought those stones are evil because they don’t look like normal stones.
Rubies having red color, were thought to be bloody stone causing death and
alexandrite which changes color from Blue/Green to red, were thought to have
mysterious power. Therefore after arrival of Christianity, the Christians took those
stones to the priests (missionaries) to play for them and curse the devil not to bring
again those wicked stones. The priests were baffled and tell the Christians to keep
bringing those evil stones……..!! Knowledge is power, be the first to get knowledge in
every field, you never know when it will ripe.
G
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Philosophy of Gem Business and Diamond Poem
For Gem Business Illiterates;
Gem Business is like Politics,
And,
Politics is like Gem Business.
Most of the People buy Gems by just trusting the seller about the benefits and features
of the merchandise (blind purchase concept). The Gem might be real or fake but they
just trust the seller’s words and close a deal. Politics is the same; you just trust the
politician’s words and vote for him/her. Both politics and Gem Business share the
same trait…..’Trust.’
But for Gem Business Literates;
Gem Business is a Science
And,
Science means Reality
Gems knowledge is a science which can be proved and confirmed, hence distinguished
from politics. The one with knowledge of gemstones is equipped with different skills to
identify and confirm what kind of jewelry/gem is. For him/her is not about trust but
reality. The only way to get this science is either to join a college or through private
studies, and get rid of being one of those who buy or deal with jewelry/gemstones
blindly. Devote your time and go through the whole compilation and for sure you will
definitely become ‘Gem Literate’.
Diamond Poem
Diamond is Durable than any gem,
Diamond is the most Desirable gem among others. And above all
Diamond is a real Deal. And for sure;
Diamond will never in any case let you into Desperation.
© Eng. Gilay Charles Shamika
2013 Sharing With Community
IMPORTANT TERMS IN GEMSTONES
COLOR
In science color is a result of light wavelength when an object’s surface responds to
light. The object’s surface can absorb, transmit or reflect light. These responses are
the ones which results to the color we see. Human being can only see wavelength
between 750 and 380nm.In gemstones, color is the combination of hue, tone and
saturation.
Colored stones as the name itself signifies, color is the supreme criteria in judging and
grading colored stone. The hue, saturation and tone in their totality pave a way to a
premium.GIA has done a great job in expressing the real differences of those three
terms and how to identify them.
Hue: Hue is the color that we notice immediately like red, blue, yellow, or green.
Saturation is the intensity of the hue present in a color sensation. Colors of low
saturation are sometimes called weak, grayish or brownish while those of high
saturation are said to be highly saturated, strong or vivid. Saturation and Tone are
used to distinguish the ‘range of colors’ (range of hue) –is it deep blue, pure Blue or
slightly Blue.
Tone indicates the lightness or darkness of a color sensation. The scale ranges from 0
for pure black to 10 for pure white. Black and white and the grays between them are
called neutral colors. They have no hue. Colors that have a hue are called chromatic
colors. Colors that do not have a hue are known as achromatic.
In ancient histories color is related with happiness, grief, sorrow or misfortunes. In
Bible and Qur’an color also signifies something according to scriptures. In different
ceremonies colour is the one which determine the event at glance. Once you see black
colour and large crowd of people, you start thinking of something wrong. The flags of
nations have different colours not by accident but they hold the means and ways of
the struggle movements towards the independence.
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For colored stones; color is the one which mostly bear the value of a particular
gemstone followed by other factors- 4Cs.
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TRANSPARENCY
In common English a word transparency means Clearness, Simplicity, Openly,
Explicitly, Precision and Intelligibility. For English natives it might mean different but
the logic remains the same. The word ‘Transparency’ has gained momentum in
contemporary politics both in international and national forums. It is either related to
democracy or administration, for instance transparency in democracy practices or
transparency in administrative decisions.
Scientifically transparency means ability of material to transmit light. The gemstones
which allow light to pass through and enable observer to see through (clear), the
gemstones are said to be transparent. If totally the gemstone doesn’t allow light to
pass through is said to be opaque.
But there are other gemstones which are in between;
Transparency – Ability to transmit light
Semi-transparent – Capable of transmitting light with some distortion, so an object
viewed through the material is indistinct.
Translucent – Capable of transmitting and diffusing light so an object viewed through
the material cannot be distinguished.
Semi-translucent – Capable of transmitting light only through thin area usually at
the edge.
Opaque – Inability of transmitting light.
HEFT OF GEMSTONES:
Heft means how heavy a gemstone is when you feel it in your hand. The
heaviness of a gemstone differs according to their crystal formation.
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INCLUSIONS AND PHYNOMENA
The meaning of Inclusion
The inclusions are virtually materials other than original gemstones. They may be
formed before, after or on the same time with the gemstones. Broadly is defined as;
Any irregularity or dislocations in a crystal's lattice, or structure, marks of the
crystallization phases, color striations, and internal fractures, which may be caused
by internal stress or external pressure; Simply the material trapped within the body of
a crystal which is different from the primary elements of the host crystal.
Types of inclusions commonly found in gemstones
Crystal’s feathers, needle like, cracks, healed fractures and included lily pads and foils.
Individual pinpoints, included crystals, voids Clusters of included crystals, or voids Clouds of pinpoints
There are three types of inclusions, or processes, through which other materials can get into a crystal;
Protogenetic Inclusions: These inclusions were already present before the host mineral was formed. The host mineral grew around them. Therefore they are older than the host crystal.
Syngenetic Inclusions: Formed at the same time as the host mineral. These inclusions can be solids, liquids, or gases, or combinations of any of the three forms of matter. These inclusions are therefore the same age as the host crystal.
Epigenetic Inclusions: These inclusions were formed after the host crystal was formed. These inclusions are usually either formed by exsolution or from the recrystallization of a fracture in a host mineral. They may also be liquid, solid, or gaseous. These inclusions are therefore younger than the host crystal.
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PHENOMENA
Phenomena are unusual display of gemstones in response to light. It is optical effects
caused by reflection, interference or refraction. The phenomena effects increase the
price of the gemstones; customers like buying something two-in-one, normal gemstone
and phenomenal gemstone when light is directed on a gemstone.
Types of Phenomena Effects
Asterism: Appearance of a star on the surface of a gem when light reflecting from
minute needle-like inclusions in a gem.
Adularescence: Appearance of blue-white light in moonstone caused by thin fibrous
or layers in moonstone by diffracting, diffusing and interfering the light.
Aventurescence: Appearance of glittering spots of color caused by light reflections
due to platelets inclusions.
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Chatoyancy: Appearance of cat’s eye resemblance on gemstone surface after light
being reflected by minute parallel needle-like inclusions, fibrous or parallel tubes
inclusions depending on the gemstones. In other word; Phenomenon of certain Cat's
eye minerals which causes them to exhibit a concentrated narrow band of reflected
light across the center of the mineral. Chatoyancy is almost exclusively exhibited on
polished cabochons.
Color change: Change of color of a gemstone body when different sources of light are
applied (incandescent and fluorescent).
Play-of-color: Appearance of flashes of spectral colors (rainbow colors) in opal when
minute silica spheres in opal cause diffraction interference of light.
Iridescence: Appearance of interference colors seen in agates and other gemstones.
But mostly, the term is for agates.
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Orient: Orient logically is iridescence phenomenon but when occur in pearls, is called
orient. Therefore orient is iridescence in pearl.
Labradorescence: Appearance of broad color flash across the surface of Labradorite
feldspar. This occurs when the thin layers in Labradorite cause light interference.
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REFRACTIVE INDEX (RI)
Refractive Index (RI) is the ration of speed of light in the air (vacuum) to the speed of
light in a medium.
SINGLE REFLECTION (SR): Is the optic property of a gemstone to exhibits a single
reading on the refractometer. The reading does not change even if you turn the
gemstone on the refractometer. If you use the polarizing filter, when you turn the gem
under the polarizing filter, the gem’s light reflection intensity remain the same.
DOUBLE REFLECTION (DR): Is the optic property of a gemstone to exhibits a
double/more than one reading on the refractometer - the maximum and minimum
readings on the refractometer. The readings change as you turn or move the
gemstone on the refractometer. If you use the polarizing filter, when you turn the gem
under the polarizing filter, the gem’s light reflection intensity change.
GEM REFRACTIVE INDEX (RI) IS LIKE HUMAN FINGER PRINT
The RI is the most useful method in identifying gemstones. Garnet and Ruby can be
quickly distinguished by SR or DR. All Garnets are single reflective (SR) while Rubies
are double reflective (DR).
Gemstone’s RI is like finger print for human being. There is no way, a finger print of
one human being to resemble with others. The same for gemstones; each gemstone
has its own RI. It is only possible for RI of one gemstone to overlap with other
gemstones and having the same birefringence but rarely to be the same.
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GEMSTONES SURFACE APPEARANCE
Gemstones surface exhibit different appearance when cut and polished. The
differences are contributed by texture and structure of the gemstones crystal lattice-
hardness.
Luster is the term used to describe how does the surface of faceted gemstone look like
in reflected light.
High luster: The gem surface shines like mirror. This includes diamond, hematite,
and Zircon and demantoid garnet.
Hematite luster is called Metallic: Mirror like luster
Diamond Luster is called Adamantine: the highest luster for all transparent gems
Demantoid garnet and Zircon Luster is called Sub adamantine: Not sharp like
adamantine.
Medium luster: The gem surface shines like glass or slightly like glass (Vitrous and
Sub-vitrous).Most transparent gemstones belong to this luster.
Low luster: The gem surface looks like Greasy, Resinous, Waxy and Dull.
Sheen Luster: The shines of the gem occur just below the gems surface. The reflection
is seen as if is inside the gem surface and look Silky/ Pearly.
SYNTHETICS AND SIMULANTS
Simulant means naturally look like. These are gems which occur naturally and used
to imitate other gemstones. For example colorless natural sapphire, quartz, topaz and
rocky crystal are sometime used as diamond simulant, while;
Synthetics are manmade gemstones with the same chemical and physical properties
as natural gemstones they imitate. They are made in Laboratory.
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GEOMETRY OF ROUGH GEMSTONES
1. Meaning of Geometry in mathematics
In mathematics geometry topic is among the difficulty. Is about how angles are related
to shapes, area and lengths of an object. I remember in my Ordinary and high school
it takes ages of time to understand this topic; especially the logic behind Angle of sine,
cosine, tangents etc.
The scientists also have taken centuries to find the simplicity of geometry calculation.
The most complicated geometry involves curved, domed and circular objects. The early
mathematicians struggled a lot and some discovered pie (π), Angle of sine, cosine,
tangents and other constants to simplify geometry of those complicated objects. The
discovery of Calculus to some extent makes life easy but for others is even worse……..!
Archimedes takes not less than 20 years to find geometry of curved objects but he was
killed before he completed his work. When roman police came to arrest him he said
‘please do anything to me but don’t disturb my circles’. His room was full of
drawings of curved objects trying to find the easy way of calculating angles, areas and
lengths. Curved and hanging bridges, domed and curved buildings, enjoy this topic in
engineering and architectural calculation before erected.
2. Meaning of Geometry in Gemstones
In gemstones, geometry means the same as in mathematics. It means a shape of
rough gemstones (crystal shape). Each rough gemstone has its habit naturally
(crystal shape). The occurrence of Moonstone shape is expected to be different from
corundum and other gemstones.
There are occurrences of seven crystal systems (shapes) in gemstone as summarized
in the next pages;
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Source: http://www.realgems.org
1. Cubic or Isometric – It is assumed all sides and length to be the same but not
always. Sometime octahedrons (eight faces) and dodecahedrons (10 faces) are
found into this crystal shape.
2. Tetragonal - similar to cubic crystals, but longer along one axis than the other, forming double pyramids and prisms.
3. Orthorhombic - like tetragonal crystals except not square in cross section (when viewing the crystal on end), forming rhombic prisms or dipyramids (two pyramids stuck together).
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4. Hexagonal - six-sided prisms. When you look at the crystal on-end, the cross section is a hexagon.
5. Trigonal - possess a single 3-fold axis of rotation instead of the 6-fold axis of the hexagonal division.
6. Triclinic - usually not symmetrical from one side to the other, which can lead to some fairly strange shapes.
7. Monoclinic - like skewed tetragonal crystals, often forming prisms and double
pyramids. This is a very simplified view of crystal structures
Some example of roughs with typical crystal system
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RUBY BACKGROUND
uby Name History: The name ruby comes from Latin word ruber, which
means red. In Sanskrit which is Indian language, ruby is termed as ratnaraj
which means King of Gems.
Colour Ranges: Ruby comes from Corundum group. According to GIA, for the
corundum to be called ruby, it should be deep, pure vivid red. This depends on the
combination of hue, tone and saturation. But in other geographical area even pinkish,
purplish or orange red sapphire are called rubies. Therefore the distinction depends
on the geographical areas. But professionally deep, pure, vivid red is ruby.
Varieties: Ruby and Sapphire are varieties of Corundum group. The difference is
colour. Ruby is red while sapphire is Blue. Sapphire has other fancy colours, like
Songea Orange colour, etc.
GEM IDENTITIES AND GEOMETRY OF ROUGH
Refractive Index (RI): DR 1.762 to 1.770 Specific gravity (SG): 4.00 Hardness: 9 Moh’s scale Inclusions: needle like rutile inclusion, fingerprint inclusions, high or low relief inclusions, two phase inclusion, straight and hexagonal growth banding, angular color banding and twining lines.
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TREATMENT
Heating: To improve color or clarity appearance
Lattice diffusion: This is a process of heating ruby to very high temperature in the
presence of a coloring agent. The aim is either to increase colour appearance, remove
color or change to other colour.
Fracture filling: Is a process of filling fractures of ruby by using oil or proxy resin.
The purpose is to improve clarity and also hide fractures.
Cavity filling: Is the same as fracture filling but cavity is large and filling it may result
in weight addition.
SYNTHETICS/SIMULANTS/IMITATION
Imitation: Glass
Confuse with: Spinel, Tourmaline, Garnets, Topaz
RUBY DEPOSITS IN TANZANIA
Morogoro: Mwalazi, Ngongolo, Matabe, Mayote,
Mvomero,Matombo,ulanga(chipa,mahenge,Lukande,Epauko)
Dodoma: Winza, Malamo, Madengi,matumbulu,mlali,mleha,Kongwa(pandambili) and Mangalisa
Tanga: Kalalani, Kofi Mountains and Umber River valley
Manyara: Hanang (dudumera), Monduli ,Mundarara
Kilimanjaro: Same (Lolobukoand North pare Mts)
Pwani: Bagamoyo(mandera)
Ruvuma: Mbinga (Likombe)
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SAPPHIRE BACKGROUND
apphire Name History: Sapphire name originates from Greek work Sappheiros.
Before Greeks mixed lapis lazuli and blue sapphire with one name ‘Sappheiros’
because both have the same color.
Color Ranges: Sapphire has many colours but when the word Sapphire is used alone
it means sapphire with blue colour. Sapphire with other colour than blue (fancy
sapphire) need to have pre-fix of color for instance, Orange sapphire, Pink sapphire,
Purple sapphire.
Varieties: Sapphire is a variety of Corundum with the same geological properties like
ruby the difference being only colour. Ruby red while sapphire Blue and other colours
– fancy sapphires (orange, pink, purple, colorless, grayish etc). The Orange sapphire
from Songea Tanzania is among the expensive fancy sapphire after pink.
GEM IDENTITIES AND GEOMETRY OF ROUGH
Refractive Index (RI): 1.762 to 1.770 Specific gravity (SG): 4.00 Hardness: 9 Moh’s scale Inclusions: needle like rutile inclusion, fingerprint inclusions, high or low relief inclusions, two phase inclusion, straight and hexagonal growth banding, angular color banding and twining lines.
TREATMENT
Heating: To improve color or clarity appearance
Lattice diffusion: This is a process of heating sapphire to very high temperature in
the presence of a coloring agent. The aim is either to increase colour appearance,
remove color or change to other colour. It creates any colour in Corundum.
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Irradiation: This bombardment of electrons which cause energy release. The process
is used to change colorless corundum to yellow or orange. But the color is not
permanent. It fades with time.
Fracture filling: Is a process of filling fractures of ruby by using oil or proxy resin.
The purpose is to improve clarity and also hide fractures.
Cavity filling: Is the same as fracture filling but cavity is large and filling it may result
in weight addition.
SYNTHETICS/SIMULANTS/IMITATION
Imitation: Glass
Synthetics: Flame fusion sapphire, Flux sapphire, Hydrothermal sapphire, Floating zone
sapphire.
Confuse with: Amethyst, Kunzite, Tanzanite, Spinel, Zircon, Topaz, Tourmaline, dAquamarine.Chrysoberyl, etc
Fancy Sapphire Confuse with: Citrine, Alexandrite, Rhodolite garnet, Spessartite garnet, Malaya garnet.
SAPPHIRE DEPOSITS IN TANZANIA
Lindi: Nachingwea Lumesule, Tunduru
Morogoro: Mahenge
Tanga: Umba valley
Dodoma: Winza
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EMERALD BACKGROUND
merald Name History: The name comes from Greek word meaning green
Color Ranges: Emerald has only green color; it is a beryl with green color.
Variety: Emerald belongs to beryl group which has two varieties – Emerald and
Aquamarine. Aquamarine is a blue beryl while Emerald is a green beryl.
GEM IDENTITIES AND GEOMETRY OF ROUGH
Refractive Index (RI): DR 1.577 to 1.583 Specific gravity (SG): 2.72 Inclusions: the gem with the most cracks and inclusions; three and two-phase inclusions, fingerprint inclusions, liquid filled inclusions, tube and needle like inclusions, calcite inclusions, angular growth zoning, minerals/crystals inclusions. Hardness: 7.5 to 8
TREATMENT
Fracture filling: filling surface-reaching fractures with colorless oils or resins. Almost
95% of Emeralds are fracture filled because the occurrence of emerald is associated
with fractures and inclusions.
SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES
Imitation: Green glass, Synthetic spinel triplet
Synthetic: Flux emeralds, hydrothermal emeralds
Alternatives: Demantoid garnet, Tourmaline, Diopside, Jadeite, Peridot, Zircon,
Tsavorite garnet, Alexandrite
EMERALD DEPOSITS IN TANZANIA:
Manyara: Mbulu Kagera: Karagwe –kyerwa
Morogoro: Mt. Nguru Rukwa: Sumbawanga-Mponda
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AQUAMARINE BACKGROUND
quamarine Name History: Latin name –water of the see due to its color being
the same as seawater – light blue.
Color Ranges: ranges from light blue to dark blue and blue-green
GEM IDENTITIES AND GEOMETRY OF ROUGH
Refractive Index (RI): DR 1.577 to 1.583 Specific gravity (SG): 2.72 Inclusions: hollow or liquid filled tubes, fingerprints and two/three phase inclusions. It occurs also as eye-clean Hardness: 7.5 to 8
TREATMENT
Heat treatment change light color aquamarine to get the desired dark blue
aquamarine.
Confuse with: Topaz, Kyanite, Tourmaline and Zircon
AQUAMARINE DEPOSITS IN TANZANIA:
Ruvuma: Tunduru
Manyara: Mbulu
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ZIRCON BACKGROUND
ircon Name History: Persian language – golden colored
Color Ranges: It has wide range of color- colorless, strong blue, green-blue, yellow,
brown, orange, red, violet. The most occurrences are strong blue and green-blue with
green color component.
GEM IDENTITIES AND GEOMETRY OF ROUGH
There are two types of Zircon - Higher and Lower Zircon. Blue zircon is said to be with high properties – strong doubling and high RI. Green zircon is said to be with low properties – no doubling and may show SR with SG 4.5 to 4.70 or 3.95 to 4.20. Refractive Index (RI): DR OTL Specific gravity (SG): 3.90 to 4.73 Inclusions: any natural inclusions possible Hardness: 6.5 to 7.5 Spectrum: Zircon with blue hue usually shows a key line at 653.5nm (known as
zircon line) with other lines up to 40’s.
Confuse with: Aquamarine, Topaz, Chrysoberyl, Tourmaline, Idocrase, Demantoid,
Hessonite, Diamond and Sapphire
ZIRCON DEPOSITS IN TANZANIA
Singida Kiomboi Iramba and Eshamwala
Morogoro: Ulanga
Tanga: Mashewa and Mavumbi
Dodoma: Winza Mpwapwa
Rukwa: Namanyere and Paramawe
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KYANITE BACKGROUND
yanite Name History: Kyanite means blue.
Color Range: Kyanite has most occurrence color is Strong blue, sometime with tints of
purple. It rarely also occur as colorless, blue-green to brown.
GEM IDENTITIES AND GEOMETRY OF ROUGH
Refractive Index (RI): DR 1.716 to 1.731 Specific gravity (SG): 3.5 to 3.7 Inclusions: Any natural inclusions possible Hardness: 4.5 to 5.0 Moh’s scale
Confuse with: Sapphire, Tanzanite and Amethyst
KYANITE DEPOSITS IN TANZANIA
Arusha: Monduli.Manyara: Kwaraha and Sidi Hill
Morogoro: Idibo Kilosa
Tanga: Makalingi, Kitwai, Hakichoo, Gologolo
Kilimanjaro: Hedaru, Chabaruti, Chankunku
Rukwa: Namanyere, Tambaluka, Kisi, Chala.
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TANZANITE BACKGROUND
anzanite Name History: Since Tanzanite is only found in one source in the
world, Tanzania East Africa. Tiffany & Co the main distributor decided to name
it by referring to the country of origin.
Colour Ranges: Tanzanite crystal occurs as a transparent rough with different colours
including brown, blue, greenish-blue and khaki. But the most common is the one with
blue colour. Predominantly blue tanzanite is generally worth more than other hues.
The deep blue (A- grade) is obtained by heating tanzanite in controlled temperature
but also they occur naturally.
Tanzanite has distinguished property of showing three colors at different angles
(Trichrinic)
Varieties: tanzanite comes from Zoisite group. Before discovery of Tanzanite the only
Zoisite varieties known were Thulite and Anyolite.
GEM IDENTITIES AND GEOMETRY OF ROUGH
Refractive Index (RI): DR 1.69 to 1.70 Specific gravity (SG): 3.35 Inclusions: Often inclusion free but can include fine needles, pinpoints and clouds. Hardness: 6.5 to 7
TREATMENT
Heating: Produce colors that include light to dark Violetish blue and bluish purple, as
well as pure blue. But these colors also occur naturally.
Confuse with: Sapphire, Kyanite, Amethyst
TANZANITE DEPOSITS IN TANZANIA:
Manyara: Merelani Tanzania
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TOURMALINE BACKGROUND
ourmaline Name History: Tourmaline name comes from toramalli which
means mixed gems in Sinhalese language of Sri Lanka.
Color Ranges: Tourmaline comes in a wide range of colors. It is believed to be a gem
with widest color ranges of any gem species.
Varieties: Tourmaline exists in six varieties categorized by their colours.
1. Rubellite tourmaline 2.Indicolite tourmaline
3. Chrome tourmaline 4.Parti-colored tourmalines
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5. Watermelon tourmaline 6. Paraiba tourmaline
GEM IDENTITIES AND GEOMETRY OF ROUGH
Refractive Index (RI): DR 1.624 to 1.644 Specific gravity (SG): 3.06 Inclusions: color zoning, thread like inclusions, gas filled fractures. Hardness: 7 to 7.5 Moh’s scale
SYNTHETICS/SIMULANTS/IMITATION:
Glass, Synthetic Ruby, Synthetic Sapphire, Synthetic Spinel
Confuse with: Any gemstones because tourmaline has all colors.
TOURMALINE DEPOSITS IN TANZANIA:
Kagera: Karagwe –kyerwa
Dodoma: Mpwapwa-Winza, Chamwino (Hombolo)
Mtwara: Newala
Tanga: Handeni-Makwere, Muheza (Ng’ombeni)
Manyara: Kiteto
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ALEXANDRITE BACKGROUND
lexandrite Name History: Alexandrite was first discovered in Russia in the
early 1800's. It was named in honor of Alexander Nicholavich, who was later to
become the Russian Czar Alexander II. Legend has it that the gemstone was
discovered on the future Czar's birthday and named in his honor, though the
factual nature of this is disputed.
Color Ranges: Blue in daylight and red/purple in incandescent light. Alexandrite is
the highly regarded color changing variety of Chrysoberyl. The color of Alexandrite
changes under different lighting conditions. If viewed in daylight, its color is greenish
blue to dark yellow-green. If viewed in incandescent or candle light, its color is pink to
red. Alexandrite is a very rare and highly valuable gemstone, and until recently was
extremely difficult to obtain due to its rarity. However, new sources in Brazil and
Tanzania have made this gemstone available and more mainstream on the gemstone
market.
GEM IDENTITIES AND GEOMETRY OF ROUGH
Refractive Index (RI): DR 1.744 to 1.755 Specific gravity (SG): 3.5 to 3.80 Inclusion: Not diagnostic – any inclusion possible. Hardness: 8.5
Confuse with: Color change Sapphire and color change Garnet
ALEXANDRITE DEPOSITS IN TANZANIA
Ruvuma: Tunduru
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CHRYSOBERYL BACKGROUND
hrysoberyl Name History: Chrysoberyl is a hard, tough, and durable gem.
Although lacking the fire of other gemstones, Chrysoberyl in its various
forms can be quite valuable.
Color Ranges: Most Chrysoberyl gems are yellow, though some are brown, green, or
orange.
Varieties: Chrysoberyl is best known for its important varieties Alexandrite and Cat's
Eye. Alexandrite is a rare and expensive form that exhibits different colors in natural
and artificial light. Cat's Eye is Chrysoberyl that is polished into a cabochon and
highly chatoyant, displaying a sharp line of light through the center of the stone.
GEM IDENTITIES AND GEOMETRY OF ROUGH
Refractive Index (RI): DR 1.744 to 1.755 Specific gravity (SG): 3.5 to 3.80 Inclusion: Not diagnostic – any inclusion possible. Hardness: 8.5
Confuse with: Topaz, Tourmaline, Zircon
CHRYSOBERYL DEPOSITS IN TANZANIA
Ruvuma: Tunduru
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TURQUOISE BACKGROUND
urquoise Name History: The name refers to French expression Pierre
Tourques (Turkish Stone).
Color Ranges: The color ranges from light to medium blue or greenish blue. It is often
mottled and sometimes has dark splotches. But can also occur without being mottled
or splotches.
GEM IDENTITIES AND GEOMETRY OF ROUGH;
Refractive Index (RI): 1.610 to 1.650 Specific gravity (SG): 2.74 Inclusions: mottled with dark splotches recessed below the surface. Hardness: 5 to 6 Moh’s scale TREATMENT
Impregnation with wax, plastic or dye added: To improve color, luster and
durability.
Backing with Epoxy resin: Adds thickness, strength and weight.
SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES
Imitations: Glass, Plastic, Reconstructed turquoise
Confuse with: Agate, Chrysocolla in Chalcedony, Jadeite, Lapis lazuli, Malachite and
Nephrite.
DEPOSITS IN TANZANIA
Tanga: Muheza – Gerevi-Hills
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PERIDOT BACKGROUND
eridot Name History: The name originated from Arabic word Faridat, which
means gem. It is also called Olivine or Chryolite.
Colour Ranges: Occurs as brownish or yellowish green to greenish yellow
GEM IDENTITIES AND GEOMETRY OF ROUGH;
Refractive Index (RI): DR 1.654 to 1.690 Specific gravity (SG): 3.34 Inclusion of natural Peridot: Disc like liquid and gas inclusions commonly called lily
pads. High relief black chromites crystal inclusions.
Hardness: 6.5 to 7 Moh’s scale
SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES
Imitations: Glass, Plastic, Synthetic sapphire, Synthetic Spinel
Confuse with: Demantoid garnet, Emerald, Tsavorite garnet, Zircon, Topaz,
Tourmaline, Jadeite, and Chrysoberyl.
PERIDOT DEPOSITS IN TANZANIA
Manyara: Mbulu- Kingiti Dodoma: Kibakwe Arusha: Leishaine Hill.
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APATITE BACKGROUND
patite Name History: Apatite in Greek means ‘to deceive’. Apatite confuses with
tourmaline and has RI close to tourmaline which can deceive you.
Colour Ranges: Occurs in variety of colour ranges. Colorless, Pink, Yellow, Green,
Blue and Violet. Apatite is a fairly uncommon gemstone, and you will only rarely see it
offered for sale in the typical commercial jewelry stores.
GEM IDENTITIES AND GEOMETRY OF ROUGH;
Refractive Index (RI): DR 1.634 to 1.638 Specific gravity (SG): 3.18 Inclusions of natural Apatite: crystals, needles, two and three phase inclusions.
Hardness: 5 Moh’s scale
Confuse with: Aquamarine, Topaz, Zircon, Demantoid Garnet, Tsavorite
APATITE DEPOSITS IN TANZANIA
Manyara: Hanang- Gallapo
Tanga: Korogwe-Umber Valley
Dodoma: Mpwapwa
Mbeya: Chamloto
Mtwara: Newala- Nagaga
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SPHENE BACKGROUND
phene Name History: The name sphene comes from greek word meaning wedge
since its crystal shape looks like wedge.
Colour Ranges: Sphene occurs in variety of color range from yellow, brown, green and
reddish brown.
GEM IDENTITIES AND GEOMETRY OF ROUGH;
Refractive Index (RI): DR OTL Specific gravity (SG): 3.52 Inclusions: All natural inclusions are possible
Hardness: 5 to 5.5 Moh’s scale
Confuse with: Demantoid garnet, Citrine, Apatite, and Tourmaline
SPHENE DEPOSITS IN TANZANIA
Tanga, Dodoma and Morogoro.
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TOPAZ BACKGROUND
opaz Name History; The source of word topaz comes from Greek Topazios,the
old name of an Island in Red Sea which used to be a source of Peridot. Topaz
was confused with peridot before advancement of gemstones identifications
kills.
Colour Ranges: The color ranges from Colorless, Yellow, Brown, Reddish, Pink and
Orange
Varieties: Topaz has no variety but just trade names
Imperial Topaz: Medium reddish Orange. The most expensive topaz.
Sherry Topaz: Yellowish brown or brownish yellow to Orange.name comes from the
color of sherry wine. To get rid of confusion with citrine and smoky quartz, Topaz with
this color range is also called precious topaz.
GEM IDENTITIES AND GEOMETRY OF ROUGH;
Refractive Index (RI): 1.619 to 1.627 Specific gravity (SG): 3.53 Inclusions: Two and three phase inclusions, liquid inclusions in its planes Hardness: 8 Moh’s scale
TREATMENT
Heating: Changes some yellow, Orange, brown topaz to Pink
Irradiation followed by heat: Produces various shades of blue from colorless.
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SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES
Imitations: Glass, Synthetic Sapphire, Synthetic Spinel
Confuse with: Aquamarine, Citrine, Tourmaline, Sapphire, Smoky Quartz, Hessonite
garnet, Morganite, Zircon, Kunzite, Spessartite garnet, Malaya garnet.
TOPAZ DEPOSITS IN TANZANIA
Dodoma: Winza Mpwapwa Tanga: Handeni Kwendikundi Plain
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IOLITE BACKGROUND
olite Name History: Iolite means violet in Greek language. It is also sometime called
Cordierite
Blue Iolite Purple Iolite
Color Ranges: It ranges from light to dark blue, brown and violet. Since it is
pleochroic, it shows different color from different viewing angles. Depending on the
angle, iolite appears colorless, gray or yellow. Navigators are said to use iolite as light
polarizer to locate the sun.
GEM IDENTITIES AND GEOMETRY OF ROUGH;
Refractive Index (RI): DR 1.542 to 1.551 Specific gravity (SG): 2.61 Inclusions: Hematite inclusions, natural inclusions
Hardness: 7 to 7.5 Moh’s scale
SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES
Imitation: Glass
Confuse with: Blue Topaz, Amethyst, Sapphire, Tanzanite and Purple/Blue Scapolite
IOLITE DEPOSITS IN TANZANIA
Manyara: Babati, Hanang
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SPINEL BACKGROUND
pinel Name History: The name’s origin is unknown. This is due to spinel being
under estimated and under appreciated by many people during early civilization. The
confusion of spinel with Rubies draws back its popularity by being referred to ruby. It
is among the rare gemstones and hence less known in a market.
Color Ranges: The color ranges from violet, blue, orange, red, pink and purple. Spinel
in most cases appears red and found in the same sources with rubies. It can also
appear as color change from grayish blue in daylight to purple in incandescent light.
Varieties: No variety but it is believed that Spinel is the most synthesized gem used
to imitate other gemstones in the market.
GEM IDENTITIES AND GEOMETRY OF ROUGH;
Refractive Index (RI): SR 1.718 Specific gravity (SG): 3.60 Inclusions: minute octahedral or negative crystals, alone or in fingerprint pattern;
included crystals, iron oxide staining.
Hardness: 8 Moh’s scale
SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES
Imitation: Synthetic Sapphire, Glass, Synthetic Ruby
Synthetics: Flux and Flame fusion Spinel
Confuse with: Garnets, Ruby, Tourmaline, Topaz, Aquamarine, Amethyst, and
Kunzite.
SPINEL DEPOSITS IN TANZANIA
Morogoro: Mahenge, Ulanga Dodoma: Winza Ruvuma: Tunduru
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SCAPOLITE BACKGROUND
capolite Name History: The name Scapolite is derived from the Greek words
scapos, which means rod, and lithos, which means stone. The natural crystal often
looks stick-like, hence it's name. Scapolite is a little known gemstone that can be quite
beautiful. The most common colors are a nice yellow to orange to pink or violet.
Scapolite is a distinctly fibrous gemstone and is often confused with amethyst, citrine,
Chrysoberyl and golden beryl.
Color Ranges: occur in different colors including Colorless, yellow, pink, violet
GEM IDENTITIES AND GEOMETRY OF ROUGH;
Refractive Index (RI): DR 1.550 to 1.564 Specific gravity (SG): 2.60 to 2.68 Inclusions: Natural inclusions
Hardness: 5.5 to 6 Moh’s scale
Confuse with: Amethyst, Tanzanite, Iolite
SCAPORITE DEPOSITS IN TANZANIA
Dodoma: Imagi, Tambi
Tanga: Umba korogwe
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GARNET BACKGROUNDS
During my study at Gemological Institute of America (GIA), garnet varieties
identification was one of my weakness points. I know at a glance that, it is a garnet
but which one……Pyrope, rhodolite, Almandite, Pyrope-Almandite, Hessonite etc!!
My instructor Annie did a tremendous job for me to master garnet varieties
identification. Eventually everything was on a right track and my classmates used to
tease me --- King of garnet. In my practical Exam of 20 stones, I picked up three
garnets and I was able to identify their varieties. Spectrum is the most useful tool for
garnet varieties identifications, especially for those combined garnets.
Green garnet Red garnet Mandarin garnet Mali garnet
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DEMANTOID GARNET BACKGROUND
emantoid Name History: In Dutch language, demantoid means Diamond like. It is
called diamond- like because it shows flashes of rainbow color (fire) like diamond.
Demantoid flashes are more noticeable compared to diamond.
Color Ranges: Green to yellow-green
GEM IDENTITIES AND GEOMETRY OF ROUGH;
Refractive Index (RI): SR 1.88 (OTL) Specific gravity (SG): 3.84 to 3.91 Inclusions: Mostly with horsetail like inclusion (radiating needle-like inclusions, but
not in all demantoid)
Hardness: 6.5 to 7 Moh’s scale
SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES
Imitation: Garnet and glass doublet, Colored CZ, Colored YAG
Confuse with: Emeralds, Peridot, Tsavorite garnet, Tourmaline, Green Zircon, and
Green Sapphire.
DEMANTOID DEPOSITS IN TANZANIA
No discovery at present
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TSAVORITE GARNET BACKGROUND
savorite Name History: The name refers to Kenya Tsavo National Park where the gem
is abundantly found. Merelani area apart from being the only source of Tanzanite, it
also host some Tsavorites.TanzaniteOneMining Ltd (TOML as it is called by TMAA)
encounters the Tsavorite when mining Tanzanite.
Color Ranges: The color ranges from light to intense green to yellowish green. It is
used mostly as alternative to Emeralds .Since the stone is not treated it is favored by
many customers who like green color.
GEM IDENTITIES AND GEOMETRY OF ROUGH;
Refractive Index (RI): SR 1.740 (Can be low up to 1.735 Specific gravity (SG): 3.61 Inclusions: Fingerprints, graphite platelets, liquid and minerals inclusions and healed fractures Hardness: 6.5 to 7 Moh’s scale
SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES
Imitation: Synthetic Spinel, Synthetic Emerald and Glass
Confuse with: Peridot, Tourmaline, Demantoid garnet and Emerald.
TSAVORITE DEPOSITS IN TANZANIA
Manyara: Merelani, Simanjiro -Lemshuku
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GROSSULARITE (GROSSULAR/GREEN) GARNET BACKGROUND
rossularite Name History: The name grossularite in Latin is gooseberry.
Color range: Near-colorless, Yellowish Green or green. Tsavorite and green garnet
(grossular) are all variety of grossularite. The difference is their color intensity.
Tsavorite is medium light to dark green, while grossularite is light yellowish green.
GEM IDENTITIES AND GEOMETRY OF ROUGH;
Refractive Index (RI): 1.735 to 1.759 Specific gravity (SG): 3.61 Inclusion: Fingerprints, graphite platelets, liquid and minerals inclusions and healed fractures Hardness: 7 Moh’s scale
NB: Grossularite- andradite garnet (mali garnet) is Yellowish green also with RI
1.773 to 1.779 while with RI 1.773 to 1.779 and yellow only , is also Grossularite
garnet
SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES
Imitation: Glass
Confuse with: Tsavorite, Tourmaline, Demantoid garnet and Emerald.
GREEN GARNET DEPOSITS IN TANZANIA
Manyara: Simanjiro –Lemshuku
Dodoma: Mpwapwa
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HESSONITE GARNET BACKGROUND
essonite Name History: The information about hessonite name is quite unknown.
Whatever the meaning of the name it is, hessonite is a variety of grossularite garnet
like tsavorite. It is also known as Cinamon Stone in market.
Color Ranges: medium to dark orange to yellow, yellow-green, brownish orange and
colorless.
NB: If pale call it grossularite not hessonite
GEM IDENTITIES AND GEOMETRY OF ROUGH;
Refractive Index (RI): SR 1.740 (can go up to 1.755) Specific gravity (SG): 3.61 Inclusions: heat wave effect (looks like undulating growth, burnt area or some call it scotch in water effect) and rounded crystals.
Hardness: 7 Moh’s scale
SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES
Confuse with: Citrine, Spessartite, Almandite, Zircon, Topaz, Orange Sapphire and
Fire Opal.
HESSONITE DEPOSITS IN TANZANIA
Morogoro: Kilosa, Uluguru mount, Mngazi valley, kisitwi
Tanga: Mlola Lushoto, Kilinga and Kihunza Handeni
Ruvuma: Likombe Mbinga
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SPESSARTITE GARNET BACKGROUND
pessartite Name History: The name comes from Spessart which is a district in
Bavaria State, German that was the first source of a gem.
Color Ranges: It is among garnet gem which is not red as most people know all
garnets are red – but it is not. (Always with orange component). Spessartite color
ranges from medium – light to dark Orange, yellowish, brownish or reddish Orange.
GEM IDENTITIES AND GEOMETRY OF ROUGH
Refractive Index (RI): SR 1.810 (OTL) Specific gravity (SG): 4.15 Inclusions: heat wave effect (looks like undulating growth, burnt area or some call it
scotch in water effect) and rounded crystals
Hardness: 7.25 to 7.5 Moh’s scale
SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES
Imitation: Synthetic Sapphire, Glass
Confuse with: Citrine, Fire Opal, Spinel, Topaz, Tourmaline, Malaya Garnet,
Carnelian, Amber.
SPESSARTITE DEPOSITS IN TANZANIA
Ruvuma: Likombe Mbinga
Morogoro: Kisitwi Kilosa, Kihunza, Mngazi valley, Uluguru Mts,
Tanga: Mlola Lushoto, Kilinga Handeni.
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RHODOLITE GARNET BACKGROUND
hodolite Name History: The name derived from Greek words, rhodo, rose and lithos,
meaning stone. Geologically, rhodolite is a mixture of Almandite and Pyrope garnets.
Color Ranges: predominantly purple but also occur in a range of light to dark
purplish red through reddish purple.
GEM IDENTITIES AND GEOMETRY OF ROUGH;
Refractive Index (RI): SR 1.750 to 1.780 Specific gravity (SG): 3.84 to 3.88 Inclusions: Low relief crystals, needle inclusions, zircon crystals with strain halos.
Hardness: 7.25 to 7.50 Moh’s scale
SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES
Imitation: Synthetic ruby and Glass
Confuse with: Topaz, Almandite, Pyrope, Spinel, Zircon, Tourmaline, Ruby.
RHODOLITE DEPOSITS IN TANZANIA
Manyara: Lelatema kiteto
Morogoro: Uluguru mts, Mngazi
Ruvuma: Likombe
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PYROPE GARNET BACKGROUND
yrope Name History: In Greek language, pyropos means fiery eyed. The gem was
called pyropos (fiery-eyed) because of having glowing red color. Sometime in market is
called Bohemian garnet.
Color Ranges: The color ranges from medium to dark reddish orange to purplish red.
GEM IDENTITIES AND GEOMETRY OF ROUGH;
Refractive Index (RI): SR 1.730 up to 1.750 Specific gravity (SG): 3.78 Inclusion: needle-like, crystals and irregular rounded crystals.
Hardness: 7 to 7.5 Moh’s scale
SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES
Imitation: Synthetic ruby and Glass
Confuse with: Topaz, Almandite, Rhodolite, Pyrope, Spinel, Zircon, Tourmaline, and
Ruby.
PYROPE DEPOSITS IN TANZANIA
Tanga: Mlola Lushoto and Kilinga Handeni
Dodoma: Tambi Mpwapwa
Morogoro: Kisitwi, Kihunza, Mngazi and Uluguru mts.
Ruvuma: Likombe Mbinga
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ALMANDITE GARNET BACKGROUND
Almandite Name History: The Almandite was named after the town of Alabanda in
Asia which was a center for trading and faceting gemstones from different places.
Color Ranges: The color range from orange red through red to reddish purple. It is
mostly fashioned as hollowed cabochons to increase color intensity- more reddish.
GEM IDENTITIES AND GEOMETRY OF ROUGH
Refractive Index (RI): SR 1.781 to OTL Specific gravity (SG): 4.05 Inclusion: zircon crystals having strain halos, high or low relief crystals and Needle-
like inclusions.
Hardness: 7 to 7.5 Moh’s scale
SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES
Imitation: Garnet- and- glass doublet
Confuse with: Hessonite, Spessartite, Rhodolite, Pyrope, Spinel, Tourmaline, Ruby.
ALMANDITE GARNET DEPOSITS IN TANZANIA
Tanga: Mlola Lushoto and Kilinga Handeni
Morogoro: Kisitwi, Kihunza, Mngazi and Uluguru mts.
Ruvuma: Likombe Mbinga
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OPAL BACKGROUND
Opal Name History: Opal is the most colorful of gems. Its splendid play of color is
unsurpassed, and fine examples can even be more valuable than Diamond. The play of
color consists of iridescent color flashes that change with the angle at which the stone
is viewed. This phenomenon is often called opalescence. The play of color may consist
of large, individual flashes of color (known as schillers), or may be of tiny, dense
flashes. The intensity and distribution of the color flashes is a determining factor in
the value of an Opal.
Color Ranges: White, Colorless, Blue, Red, Green, Yellow, Orange, Brown, Pink,
Purple, Gray, Black, Banded, and Multicolored.
TYPES OF OPAL:
Opals are classified into two types; Precious Opal and Common Opal.
Opals displaying play of color are known as Precious Opals, and opals lacking play of
color are known as Common Opals.
Varieties of Opal: There are many varieties of both precious and common Opals.
Black Opal: Is the most desired and beautiful form of opal. It is opal with a dark blue,
dark green or black background with a strong play of color.
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White Opal: Opal with a light colored body color (white, yellow, cream, etc.) with
strong play of color.
Fire Opal: Opal with a transparent to translucent deep-orange red. Mostly fire opal
does not show play of color. If Fire Opal displays play of color, it is then called
Precious Fire Opal.
Opal Doublets and Triplets
Opal Doublets: Are thin slices of precious opal glued onto a base with any material to
increase hardness of opal.
Black layer glued onto a base.
Opal Triplets: Are like opal doublets but coated with a thin layer or dome of clear
Quartz on top of cabochon to make them more resistant to scratches. (Glued on
bottom and on Top covered with thin layer of other transparent materials)
Black layer onto a base and thin transparent on top glued
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Crazing Problem: A condition whereby opal shows cracks internally or on the surface
when opal loose moisture. It is advised to keep opal away from excessive temperature.
But not all opals are affected by crazing.
GEM IDENTITIES AND GEOMETRY OF ROUGH
Refractive Index (RI): SR 1.450 Specific gravity (SG): 2.15 Inclusion: patches or dots of play of color. The pattern maybe in terms of small dots
(pin fire), large patches (flash) or distinct patches known as harlequin.
Hardness: 5.5 to 6.5 Moh’s scale
SYNTHETICS:
Gilson synthetic opal or other synthetic opal, under magnification they show
snakeskin-like structure or known as chicken wire pattern. Synthetic opal also can
show columnar structure vertically.
OPAL DEPOSIT IN TANZANIA
Kigoma: Buhoro, Nyakitonto and Makere
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MALACHITE BACKGROUND
Malachite Name History: The stone's name derives from Greek molochitis lithos,
"mallow-green stone”. The mineral was given this name due to its resemblance to the
leaves of the Mallow plant.
Color Ranges: green, bluish-green or greenish blue with bands
GEM IDENTITIES AND GEOMETRY OF ROUGH
Refractive Index (RI): AGG 1.655 to OTL (use birefringence blink method) Specific gravity (SG): 3.95 Inclusion: distinctive green banded appearance
Hardness: 3.5 to 4 Moh’s scale
SYNTHETICS/SIMULANTS/IMITATION/
Imitation: Glass, plastic
Confuse with: Turquoise, Jadeite, Nephrite
MALACHITE DEPOSITS IN TANZANIA
Dodoma: Winza
Rukwa: Mpanda
Mara: Kamba Hill Tarime
Mtwara: Masasi Ntaka
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FLUORITE BACKGROUND
luorite Name History: Latin meaning flow.
Color Ranges: It ranges from yellow, green, blue and purple. Purple or blue are mostly
banded with colorless bands.
GEM IDENTITIES AND GEOMETRY OF ROUGH;
Refractive Index (RI): SR 1.43 Specific gravity (SG): 3.18 NET Inclusion: Color Zoning or Bands, it might be also parti-colored, all inclusions
Hardness: 4 Moh’s scale
Confuse with: Since fluorite has every color, it confuse with any gemstone.
FLUORITE DEPOSITS IN TANZANIA
Mbeya: Chunya, Tukuyu
Rukwa: Mpanda
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MOONSTONE BACKGROUND
oonstone Name History: It is called moonstone because it has a white
shimmer like moonshine. That optic effect is called adularescence. It can
also show asterism (star effect)
Color Ranges: It is colorless to white with a whitish-silvery to bluish sheen called
adularescence (bluish sheen against colorless body.)But can be orange, yellow or
brown.
Varieties: There are two moonstone varieties, Moonstone Orthoclase and Moonstone
Labradorite
Moonstone Orthoclase – blue sheen with colorless body while
Moonstone Labradorite – sometime called rainbow moonstone, it has strong blue or
multi-color sheen.
GEM IDENTITIES AND GEOMETRY OF ROUGH;
Refractive Index (RI): DR/AGG 1.518 to 1.526 Specific gravity (SG): 2.58 Inclusion: centipede like inclusions
Hardness: 6 to 6.5 Moh’s scale
Confuse With: Blue chalcedony and glass imitation
MOONSTONE DEPOSITS IN TANZANIA
Morogoro: Kilosa Gairo
Dodoma: Mkoyo and Zoisa Kondoa
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SUNSTONE BACKGROUND
Sunstone Name History: The name refers to the color and glitteriest of the
gemstone which look-like the sun.
Color ranges: The sunstone has different varieties but the common one is
orange.
GEM IDENTITIES AND GEOMETRY OF ROUGH;
Refractive Index (RI): DR/AGG 1.539 to 1.547 (sunstone Oligoclase) 1.518 to 1.526 (sunstone Orthoclase) Specific gravity (SG): 2.65/2.58 (sunstone Oligoclase/ sunstone Orthoclase) Inclusion: Reddish to Golden metallic platelets
Hardness: 6 to 6.5 Moh’s scale
Varieties: There are two varieties of Sunstone. Sunstone Oligoclase and Sunstone
Orthoclase
Confuse with: Glass imitation, Plastic imitation
SUNSTONE DEPOSIT IN TANZANIA
Morogoro: Mtimbila Mahenge and Kilosa Gairo
Tanga: Mtae Hill Lushoto
Kilimanjaro: Ugweno Mwanga
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AMAZONITE BACKGROUND
mazonite Name History : comes from amazone forest where it is believed
to be mined for the first time commercially.
Color Ranges : Green to Greenish- blue
GEM IDENTITIES AND GEOMETRY OF ROUGH;
Refractive Index (RI): AGG 1.522 to 1.530 Specific gravity (SG): 2.56 to 2.58 Inclusion: mottled coloring with grid-like patterns
Hardness: 6 to 6.5 Moh’s scale
Confuse with: Chalcedony, Chrysoprase, Serpentine and Turquoise
AMAZONITE DEPOSITS IN TANZANIA
Tanga : Luguruni handeni
Morogoro : Kilosa Gairo
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LABRADORITE BACKGROUND
Labradorite Name History: It was first discovered in Labrador, Canada and named
after that area.
Color Ranges: Labradorite is a member of the Feldspar family with remarkable play of
color, known as Labradorescence. The color usually ranges from gray-green, dark
gray, black or grayish-white. Labradorite is composed in aggregate layers that refract
light as iridescent flashes of peacock blue, gold, pale green or coppery red. The
predominant blue varies within the light, displaying hues from deepest blue to various
shades of pale, almost blue-green.
GEM IDENTITIES AND GEOMETRY OF ROUGH;
Refractive Index (RI): AGG/DR 1.559 to 1.568 Specific gravity (SG): 2.70 Inclusion: Black-needle like inclusions, metallic looking platelets which cause
Labradorescence and repeated twinning.
Hardness: 6 to 6.5 Moh’s scale
Confuse with: Rainbow moonstone
LABRADORITE DEPOSITS IN TANZANIA
Kigoma: Kidahwe, Nyakitonto
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QUARTZ BACKGROUND
Quartz is among abundant gemstones on earth. The abundance of quartz is due to its
formation, it is made by silica and oxygen (silicate oxide - SiO2). Since silica and
oxygen are found everywhere on earth, quartz is also found everywhere.
The formation of quartz varieties depends on the size of the silica (clay) which
combines with oxygen in presence of favorable temperature and water. The silicate
crystallizes either in macro or micro depending on the silica size. Therefore, quartz
varieties are divided into two groups; Macro – crystalline quartz and Micro – crystalline
quartz.
NB: All quartz varieties are Uniaxial positive; Might show a bull’s eye or Airy’s spiral optic figure.
Quartz also shows brazil-law twinning under crossed polarizing filters.
Macro- Crystalline Quartz Micro – Crystalline Quartz
Rose quartz, Chalcedony ;
Citrine Chrysoprase
Amethyst Chrysocolla-in- chalcedony
Rock Crystal Onyx, Carnelian
Smoky quarts Agate ,Iris agate, Fire agate, Dendritic agate
Aventurine quartz Bloodstone
Jasper
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ROSE QUARTZ BACKGROUND
Name History: It is called rose quartz simply because, the color looks like rose flower.
Color Ranges: The color of rose quartz ranges from very light to medium dark pink.
GEM IDENTITIES AND GEOMETRY OF ROUGH
Refractive Index (RI): DR 1.544 to 1.553 Specific gravity (SG): 2.66 Inclusion: look cloudy due to fracture, never transparent (semitransparent to
translucent)
Hardness: 7 Moh’s scale
SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES
Imitation: Glass and Plastic
Alternatives: Topaz, Spinel, Tourmaline, Ruby.
ROSE QUARTZ DEPOSITS IN TANZANIA
Kigoma: Mbirira Kasulu
Dodoma: Winza Mpwapwa
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CITRINE QUARTZ BACKGROUND
itrine Name History: The name citrine is related to citrus fruit’s color.
Color Ranges: The color of citrine ranges from light golden yellow to reddish yellow.
Most people confuse citrine with topaz of similar color.
GEM IDENTITIES AND GEOMETRY OF ROUGH;
Refractive Index (RI): DR 1.544 to 1.553 Specific gravity (SG): 2.66 Inclusion: Color zoning, negative crystals, two and three phase inclusion, twinning
Hardness: 7 Moh’s scale
SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES
Imitation: Glass and Plastic
Synthetics: Synthetic hydrothermal quartz, Synthetic sapphire, Synthetic Spinel
Confuse with: Topaz, Spessartite, Orange Sapphire, Carnelian, Amber, Chrysoberyl,
and Tourmaline.
CITRINE QUARTZ DEPOSITS IN TANZANIA
Morogoro: Rubeho Kilosa
Dodoma: Winza Mpwapwa
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AMETHYST QUARTZ BACKGROUND
methyst Name History: No vivid information about amethyst name.
Color Ranges: The Amethyst color is purple. The finest amethyst color comes from
Africa.
GEM IDENTITIES AND GEOMETRY OF ROUGH
Refractive Index (RI): SR 1.544 to 1.553 Specific gravity (SG): 2.66 Inclusion Negative crystals, liquid, color zoning, two and three phase.
Hardness: 7 Moh’s scale
SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES
Imitation: Glass, Purple synthetic corundum, Synthetic Spinel triplets
Synthetics: Hydrothermal
Confuse with: Topaz, Spinel, Tanzanite, Sapphire, Tourmaline, Iolite, Rhodolite
garnet.
AMETHYST QUARTZ DEPOSITS IN TANZANIA
Kigoma: Mbirira Kasulu
Morogoro: Rubeho Kilosa and Tungi
Dodoma: Winza Mpwapwa
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ROCKY CRYSTAL QUARTZ
ocky Crystal Name History: It is called rocky crystal because it looks like colorless
crystal. The colorless, transparent variety of Quartz, free of any impurities, is known
as "Rock Crystal". Flawless and very large cuts may be cut from Rock Crystal.
Color Ranges: It is colorless quartz.
Name History: The name citrine is related to citrus fruit’s color.
Color Ranges: The color of citrine ranges from light golden yellow to reddish yellow.
Most people confuse citrine with topaz of similar color.
GEM IDENTITIES AND GEOMETRY OF ROUGH
Refractive Index (RI): DR 1.544 to 1.553 Specific gravity (SG): 2.66 Inclusion: needles, two and three phase inclusions, liquid crystals.
Hardness: 7 Moh’s scale
SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES
-No information at present
ROCKY CRYSTAL QUARTZ DEPOSITS IN TANZANIA
Morogoro: Rubeho Kilosa
Dodoma: Winza Mpwapwa
Kigoma: Mbirira Kasulu
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SMOKY QUARTZ BACKGROUND
Smoky Quartz Name History: Smoky Quartz is the brown "smoky" variety of
Quartz. It ranges in color from light brown to black.
Color Ranges: It ranges in color from light brown to black.
GEM IDENTITIES AND GEOMETRY OF ROUGH;
Refractive Index (RI): 1.544 to 1.553 Specific gravity (SG): 2.66 Inclusion: crystals, two and three phase inclusion, needles,
Hardness: 7 Moh’s scale
SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES
-No information at present
SMOKY QUARTZ DEPOSITS IN TANZANIA
Quartz is one of the most common and varied minerals on earth, and its abundant throughout
the country. Quartz is extremely common and is found in numerous localities throughout the
world.
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AVENTURINE QUARTZ BACKGROUND
venturine Quartz Name History: The name reflects the phenomenon effect caused
by chrome mica inclusions which cause appearance of glittering spots of color-
Aventurescence.
Color Ranges: It is almost green but rarely yellow, gray and brown.
GEM IDENTITIES AND GEOMETRY OF ROUGH
Refractive Index (RI): 1.544 to 1.553 Specific gravity (SG): 2.66 Inclusion: chrome mica inclusions (tiny, disk-like, flakes or platelets randomly
distributed) which cause Aventurescence phenomenon.
Hardness: 7 Moh’s scale
SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES
-No information at present
AVENTURINE QUARTZ DEPOSITS IN TANZANIA
Quartz is one of the most common and varied minerals on earth, and its abundant
throughout the country. Quartz is extremely common and is found in numerous
localities throughout the world.
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CHRYSOPRASE BACKGROUND
hrysoprase Name History: the name comes from Greek language, meaning gold
leek.
Color Ranges: It is almost yellowish green.
GEM IDENTITIES AND GEOMETRY OF ROUGH
Refractive Index (RI): AGG 1.530 to 1.540 Specific gravity (SG): 2.60 Inclusion: Not diagnostic
Hardness: 6.5 to 7 Moh’s scale
SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES
-No information at present
CHRYSOPRASE DEPOSITS IN TANZANIA
Dodoma: Chamwino, Itiso-Haneti
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CHALCEDONY VARIETIES BACKGROUND
GEM IDENTITIES AND GEOMETRY OF ROUGH;
Refractive Index (RI): 1.530 to 1.540 Specific gravity (SG): 2.5 to 2.6
Inclusion: curved, straight bands or layers.
Hardness: 6.5 to 7 Moh’s scale
CHALCEDONY DEPOSITS IN TANZANIA:
Dodoma: Haneti – Itiso Hill.
Kigoma: Kasulu.
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AGATE BACKGROUND
Color Ranges: All colors banded with curved or straight lines.
Varieties: moss agate, fire agate, dendritic agate, iris agate
FIRE AGATE
Refractive index (RI): AGG 1.53 to 1.54 Specific Gravity (SG): 2.60
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DENDRITIC AGATE
Refractive index (RI): AGG 1.53 to 1.54 Specific Gravity (SG): 2.60
IRIS AGATE
Refractive index (RI): AGG 1.53 to 1.54 Specific Gravity (SG): 2.60
MOSS AGATE
Refractive index (RI): AGG 1.53 to 1.54 Specific Gravity (SG): 2.60
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ONYX
Refractive index (RI): AGG 1.53 to 1.54
Specific Gravity (SG): 2.60
SARD
Refractive index (RI): AGG 1.53 to 1.54
Specific Gravity (SG): 2.60
SARDONYX
Refractive index (RI): AGG 1.53 to 1.54 Specific Gravity (SG): 2.60
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CARNELIAN
Refractive index (RI): AGG 1.53 to 1.54 Specific Gravity (SG): 2.60
CHRYSOCOLLA - IN - CHALCEDONY
Refractive index (RI): AGG 1.53 to 1.54 Specific Gravity (SG): 2.60
JASPER BACKGROUND
Refractive index (RI): AGG 1.53 to 1.54 Specific Gravity (SG): 2.60
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BLOODSTONE
Refractive index (RI): AGG 1.53 to 1.54 Specific Gravity (SG): 2.60
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PEARL BACKGROUND
earls are among the most ancient decorations used by human being.
Natural Pearl - Pearl that is formed from calcium carbonate secretions that forms naturally within a mollusk without any human intervention. This term is distinguished from the more common Cultured Pearls which are produced with human intervention.
Cultured Pearl. Cultured Pearls are produced by inserting a foreign substance known
as a nucleus within the body of an oyster or mussel, which in turn causes the
organism to grow a pearl around the nucleus. Oysters are cultivated and harvested in
mass numbers for the purpose of growing Pearls within them. Almost all Pearls
currently available on the gemstone market are of Cultured Pearl.
VARIETY OF PEARLS.
Freshwater Pearl - Pearl that grew in a non-saline environment in a freshwater mussel with a habit of forming in irregular “potato” like shapes. The most abundant form of Pearls because each mussel can produces up to 50 Pearl while saltwater oysters produce only one to three Pearls per oyster.
Saltwater Pearl - Pearl produced by a mollusk such as an oyster in a body of saltwater such as the ocean.
Akoya Pearl: Cultured Pearls with a white color and a consistent round shape and a
mirror- like metallic luster. Sometimes are treated to look black or a very dark blue.
South Sea Pearls: Pearls with large size, white and golden color
Tahitian Pearl: Also known as “Black Pearl.” They range in color from green to blue,
red, gold and black.
Abalone Pearl These pearls are often an iridescent blue color and commonly horn-shaped
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Overtone: Although Pearls are characterized by body color, they also have an
“overtone.” Overtone is the word used to describe the glint of a Pearl in various
lighting. Overtones are most apparent in saltwater pearls. Although Freshwater pearls
have an overtone, it is not as prominent or exact as those found in saltwater pearls.
PEARLS DEPOSITS IN TANZANIA
Along the Indian Ocean in Mainland and Zanzibar
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RARE BLUE STONES THAT LOOK LIKE
LAPIS LAZULI
Lapis Lazuli is a deep blue opaque gemstone with pyrite sparkling.
Refractive Index (RI): 1.50 to 1.67 Specific gravity (SG): 2.40 to 2.90
SODALITE
White streak/ irregular white lines
Refractive Index (RI): 1.483 to 1.487 Specific gravity (SG): 2.20 to 2.30
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SUGILITE
Refractive Index (RI): 1.607 to 1.610 Specific gravity (SG): 2.75 to 2.80
CHAROITE
Refractive Index (RI): 1.55 to 1.56 Specific gravity (SG): 2.50 to 2.80
AZURITE
Refractive Index (RI): 1.73 to 1.84 Specific gravity (SG): 3.75 to 3.95
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Reference
1. GIA Lab Manual
2. Gemstones of the World By Walter Schumann
3. GIA Gem Reference Guide
4. Gemstones Guide by Shazmin,2000
5. Gems Picture credits: Google gemstones picture
6. Gemstones Processing Steps by Eng. Gilay Shamika,2010
7. http://www. Minerals.net
8. http://www.realgems.org
9. http://www.gst.go.tz
10. http:// www.tmaa.go.tz
11. Philosophy of Gems Business by Eng.Gilay Shamika,2013