3.2MINERALS
WHAT IS A MINERAL?
Naturally occurring
Inorganic
Crystalline structure
Solid
Fixed chemical composition
CHARACTERISTICS OF MINERALS
All minerals contain one or more of the naturally occurring elements (about 90).
CHARACTERISTICS OF MINERALS
Earth scientists have identified more than 4000 minerals, but only about 20 of them are common.
The common minerals are called rock-forming minerals because they form the rocks making up Earth’s crust.
Of the 20 rock-forming minerals, only about half of them are so common they make up 90% of the mass of Earth’s crust.
COMMON ROCK-FORMING MINERALS
Quartz
Orthoclase (Potassium) Feldspar
Dolomite
Olivine
Halite
Muscovite Mica
Biotite Mica
Pyroxene
Calcite
Gypsum
Amphibole
Plagioclase Feldspar
MINERAL GROUPS
Silicate Minerals Minerals containing a combination of the
two most common elements in Earth’s crust, Silicon (Si) and Oxygen (O).
Make up 96% of the Earth’s crust. The basic building block of silicate minerals is the silicon-
oxygen tetrahedron, SiO4.
Non-silicate Minerals Minerals not containing a combination of Si and O. Make up remaining 4% of Earth’s crust.
- Native Elements - Sulfates- Oxides - Sulfides- Carbonates - Halides
Silicon-Oxygen Tetrahedron
CRYSTALLINE STRUCTURE
All minerals in Earth’s crust have a crystalline structure.
A crystal is a solid whose atoms, ions, or molecules are arranged in a regular, repeating pattern. Each type of mineral crystal is characterized
by a specific geometric arrangement of atoms.
Scientists can study a mineral’s crystals by using X-rays. The X-rays pass through a crystal and strike a
photographic plate producing an image showing the geometric arrangement of the atoms.
SILICATE CRYSTALLINE STRUCTURE
Silicon-oxygen tetrahedra combine in different arrangements to form different silicate minerals. This is due to the kinds of bonds forming between the oxygen atoms
of the tetrahedra and other atoms. The oxygen atoms may be shared with neighboring tetrahedra or
form with other elements outside of the tetrahedra.
There are 6 kinds of arrangements tetrahedra form:1. Isolated 4. Double-chain2. Ring 5. Sheet3. Single-chain 6. Framework
SILICATE CRYSTALLINE STRUCTURE
Example: Olivine
Example: Beryl
Example: Pyroxene
Example: Amphibole
Example: Mica
Example: Quartz, Feldspars
NON-SILICATE CRYSTALLINE STRUCTURE
Non-silicate minerals have a diverse chemical composition, thus displaying a vast variety of crystalline structures. Common ones include:
1. Cubes2. Hexagonal prisms3. Irregular masses
The crystal structure of non-silicates determine their characteristics. Example: Native elements, like Gold (Au), have very high densities
because their crystal structures are based on the packing of atoms as close together as possible, known as close-packing.
Gold
PHYSICAL PROPERTIES OF MINERALS
The physical properties of minerals include:
COLOR
LUSTER
STREAK
CLEAVAGE
FRACTURE
HARDNESS
DENSITY
SPECIAL PROPERTIES
CRYSTAL SYSTEM
COLOR
Not a reliable clue for identifying minerals.The same mineral can come in a variety of colors.
For example: Quartz
Rose Quartz
Crystalline Quartz
Milky Quartz
Amethyst Quartz
STREAK
The color of a mineral in powdered form is known as its streak.
Determined by rubbing a mineral against a piece of unglazed porcelain known as a streak plate.
LUSTER
The way the surface of a mineral reflects light is known as its luster.
When you say an object is shiny or dull, that’s luster!If a mineral is shiny like a
metal, it is considered metallic.
If a mineral is dull, it is considered to be non-metallic.
Galena Hematite
LUSTER
Non-metallic lusters include:
Vitreous (glassy)
Silky (fiber-like)
Resinous (plastic-looking)
Quartz
Satin Spar Gypsum
Orange Garnet
LUSTER
Waxy (greasy)
Adamantine (diamond-like)
Earthy (Earth-like)
Pearly (pearl-like)
Jade
Diamond
Limonite
Muscovite Mica
CLEAVAGE
The splitting of minerals along smooth, flat planes is known as cleavage.
Determined using the “sandwich” rule.
Different types include: Basal (1 plane) Prismatic (2 planes) Rhombohedral (3
planes NOT at right angles) Cubic (3
planes at right angles) Octahedral (4 planes) Dodecahedral (6 planes)
Mica – Basal Cleavage (1 plane)
Halite – Cubic Cleavage (3 planes at
right angles)
Calcite – Rhombohedral Cleavage (3 planes not at right
angles)
Fluorite – Octahedral Cleavage (4 planes)
Sphalerite – Dodecahedral
Cleavage (6 planes)
Barite – Prismatic Cleavage (2 planes)
FRACTURE
The breaking of minerals unevenly along curved, irregular, or other-shaped surfaces is known as fracture.
Different types include: Conchoidal (curved) Irregular (uneven) Fibrous (splintery) Hackly (jagged-edged)
Quartz – Conchoidal Fracture
Aerinite – Irregular Fracture
Serpentine – Fibrous Fracture
Iron – Hackly Fracture
HARDNESS
A mineral’s resistance to being scratched is considered its hardness.
To determine hardness, scientists use Moh’s Hardness Scale.
Fredrich Mohs
2.5
3.5
4.5
5.5
6.5
CRYSTAL SYSTEM
A mineral crystal forms in one of six basic systems.
Include:
Isometric (Cubic) Tetragonal Hexagonal Orthorhombic Monoclinic Triclinic
Isometric
Tetragonal
Hexagonal
Orthorhombic
Monoclinic
Triclinic
DENSITY
The ratio of the mass of a substance to the volume of the substance is called density. Usually measured in g/cm3. Most of the
common minerals in Earth’s crust have densities between 2 and 3 g/cm3.
Water has a density of 1.0 g/cm3 and is used a reference point for other substances. The ratio of an object’s density to the
density of water is called its specific gravity.
SPECIAL PROPERTIES
Some minerals have to ability to glow under ultraviolet (UV) light and exhibit fluorescence. Some continue to glow after the UV light is
turned off and this is known as phosphorescence.
Some minerals will effervesce, or “fizz”, when a drop of a weak acid (such as HCl) is placed on it.
Calcite has a special property known as double refraction, when light is bent causing an image to be doubled.
Calcite and Willemite
Chalk
Calcite
SPECIAL PROPERTIES
Magnetite and Pyrrhotite are naturally magnetic minerals attracting iron. Non-silicate minerals containing iron are
more likely to be magnetic than others without iron.
Some minerals exhibit a distinct taste, such as Halite (table salt).
Some minerals are radioactive and can be detected using a Geiger Counter device. Radioactivity results as unstable nuclei decay
over time into stable nuclei by releasing particles and energy.
Magnetite
Halite
Geiger Counter
SPECIAL PROPERTIES
In reflected light, some minerals display a silky band known as chatoyancy. Commonly called the “Cat’s Eye Effect”. Comes from the French word chat meaning
“cat” and oiel meaning “eye”. It is the result of closely packed parallel
fibers within the mineral.
A similar effect called asterism, is the phenomenon in which a six-sided star shape appears when a mineral reflects light.
Chalcedony Quartz
Cabochon Corundum
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