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Mineral Identification Labs

SILICATES AND NON-SILICATES

Mineral Labs

Sorry I was out last week. Here is a quick and dirty slide show to help with mineral identification.

What I initially look for… Luster: Metallic Vs Non-Metallic

Hardness: scratch test mineral vs fingernail, blade, quartz, topaz;

Steak color

Cleavage

Specific gravity: does it feel heavy?

Special Properties: To Fizz or Not To Fizz? Magnetic? Double Refracting…

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Lab Book

The lab book is your best friend in identification of some common rock forming minerals.

For each mineral you are expected to identify you will find an entry in the lab book listing the Form, Physical Properties, Diagnostic Criteria, Occurrence, Varieties, and Economic Uses.

Minerals are grouped into chemical composition categories.

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Non-Silicate Minerals

Native Elements

Periodic table elements

Gold, Silver, Copper, Platinum, Iron, Mercury, Lead, Palladium, Tin, Arsenic, Graphite, Diamond, Etc.

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Sulfides Minerals composed of positively

charged metals with Sulfide (S2-) anion.

Galena (PbS)

Pyrite (FeS2)

Chalcopyrite (CuFeS2)

Sphalerite (ZnS)

Sulfates

Minerals composed of positively charged metals with Sulfate (SO4

2-)anion. Gypsum (CaSO4

.2H2O)

Barite (BaSO4)

Alabaster

Barite

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Oxides

Minerals composed of positively charged metals with Oxide (O2-) and/or Hydroxide (OH-) anions.

Magnetite (Fe3O4) or (FeO) or (Fe2O3)

Hematite (Fe2O3)

Corundum (Al2O3)

Limonite (2Fe2O3.3H2O)

Halides

Minerals composed of positively charged metals with Halogen elements (F-), (Cl-), (Br-), (I-) anions. Halite (NaCl) Fluorite (CaF2)

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Carbonates

Minerals composed of positively charged metals with carbonate (CO3

-) anion. Calcite (CaCO3)

Dolomite (CaMg[CO3]2)

Aragonite(CaCO3)

Azurite (Cu3[CO3]2(OH)2

Malachite (Cu2CO3(OH)2

Phosphates

Minerals composed of positively charged metals with phosphate (PO4

3-) anion. Apatite (Ca5[PO4]3(F,Cl,OH)

Turquoise (CuAl6[PO4]4[OH]8

.4H2O

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Silicate Minerals

Silicate Minerals

Silicate minerals are the largest chemical group among minerals and by far the most common rock-forming minerals. ~90% of crustal minerals

The fundamental component of the silicate group is the silicate tetrahedra (SiO4)4-.

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Silicate Minerals

Silicates classes are differentiated by the geometry of the tetrahedra linkage, which inform crystal habit, cleavage, and other characteristics.

More silicate structure diagrams

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Nesosilicates

Inosilicates

Inosilicates

Phyllosilicates

Tectosilicates

Tectosilicates

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Feldspar Group

Crystallization here results in two feldspars

Feldspar Group

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Potassium Feldspar (K-Spar) Sanidine, Orthoclase,

Microcline. Common mineral in

felsic Ig Rk (qtz & biotite), meta gneiss, and arkosicsedimentary rocks.

Right angle cleavage Will scratch knife

blade Perthitic structures ≠

Striations!!

Sodium-Calcium FeldsparPlagioclase Solid Solution Series

NaAlSi3O8<oligoclase, andesine, labradorite, bytownite, anorthite>CaAl2Si2O8

Felsic Mafic

Striations on a perfect cleavage face are a big indicator Roughly 90º cleavage Due to solid solution series can be in almost any Ig Rk

Oligoclase Labradorite anorthite in andesine

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Mica Group

Muscovite, biotite, phlogopite, lepidolite Sheet mica = characteristic thin folia cleavage plane Very common in felsic Ig Rks and metamorphic RKs

Biotite Muscovite Lepidolite

Pyroxene Group Ca(Mg,Fe,Al)(Al,Si)2O

Single chained Silicate mineral group generally containing Ca, Mg, Fe and occasionally other substituting elements in varying amounts.

Dark Color (green to black) prismatic crystals

Greenish to black streak Near 90º cleavage H = 5.6 Common in Ig Rks

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Amphibole Grouphydrated calcium magnesium silicate

Ca2Na(Mg,FeII)4(Al,FeIII,Ti)3Si6O22(OH)

Similar to pyroxene mineral group but double chained

Double chain framework results in acute (60º) and oblique (120º) cleavage

Usually dark colored. Cleavage is diagnostic Common in Ig & MM Rks You can generally tell hornblende

from augite by cleavage and hornblende looks splintery where augite does not.

Olivine

(Mg,Fe)2SiO4

Generally granular aggregates or rounded grains

Greenish color in mafic Ig Rks is often diagnostic

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Garnet

X3Z2(SiO4)3

Most often found in dodecahedral crystals (soccer balls)

Common in MM RKs, especially Schists, High P & T environments

Can be nearly any color Diagnotic criteria include

crystal form (soccer balls, trapezahedral) and hardness (H = 6.5-7.5)

Talc hydrous magnesium silicateMg3SiO10(OH)2

Occurs from the alteration of other minerals (like pyroxenes and amphiboles)

Identified by hardness (H=1) micaceous habit, and greasy feel

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QuartzSiO2

Quartz is everywhere!! Common in felsic Ig

Rks, MM Rks, Sed Rks Identified by

conchoidal fracture, vitreous/glassy luster, and hexagonal crystal form (often with striations)

ChloriteIron-Magnesian Aluminum Silicate

(Mg,Fe)3(Si,Al)4O10(OH)2(Mg,Fe)3(OH)6 (what a nightmare!)

Common mineral in Ig and MM Rks, and is the diagnostic mineral of the green schist facies (a MM facies).

Usually greenish, but can be a variety of other colors.

Micaceous habit and Hardness (H=2-2.5)

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KaoliniteHydrous Aluminum SilicateAl2SiO5(OH) Clay mineral formed by the chemical

weathering of aluminum silicates (K-Spars) Dull and earthy luster, usually white to

yellowish, when you see it you will think “this is chalk” but chalk is a sedimentary carbonate rock and this is a silicate mineral. Chalk is more slippery when handled than kaolinite.

TopazAluminum SilicateAl2SiO4(F,OH)2

Super Hard!! H=8Also pretty heavy (G=3.4-3.6)Can look like Qtz but is much

heavier and harder (hold similar size Qtz and Topas and see for yourself)

Can be a variety of colors but is usually colorless.

Typical Topaz Rarer Varieties

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Helpful Websites for studying minerals!!

Mindat.org Minerals.net Geology.com Mineralseducationcoalition.org

Lets Get To Work