1. Minerals
Dr. R. B. Schultz

2. The earth is made of rocks, which are in turn made of minerals
The earth is made of rocks, which are in turn made of minerals. In this part of the course we'll learn how to identify common minerals and rocks.
In order for something to be classified as a mineral, it must meet five (5) criterion:
Minerals are:
·        1. Naturally occurring,
·        2. Inorganic,
·        3. Have known chemical compositions
·        4. Have definite physical properties.
5. Are solid
·       
They are usually (although not always) crystalline.

3. Moh's Hardness Scale (Commit this to memory)
 Mineral Classification
Minerals are classified based on chemical composition and crystal structure.
Minerals are made of different ions bonded together.
Ions are charged atoms
·        Cations are positively charged whereas
·        Anions are negatively charged
Common ions in earth's crust:
O - most common ion (anion)
Si, Al, Fe, Ca, Na, K, Mg, (Cations)
Minerals are made mainly of these ions
Crystal structure
Crystal structure depends on sizes of and charges on ions
Polymorphs -- same chemical composition, different crystal structures
Mafic silicate minerals
Most common minerals are silicates
All silicate minerals contain silicon and oxygen
Silicates that also contains iron or magnesium are called mafic silicate minerals
Mafic silicate minerals are dark in color
Examples: of mafic silicates: olivine, pyroxene, amphibole, and biotite mica
Felsic silicates
Felsic silicates are silicate minerals that don't contain magnesium or iron, are light in color
Examples: feldspar, quartz, clay minerals, muscovite mica
Silicate mineral structures
Basic building block: silica tetrahedron
Silica tetrahedron is a silicon ion bonded to 4 oxygen ions
Silicon is positively charged (+4)
Oxygen is negatively charged (-2)
Net charge on tetrahedron: -4
Because tetrahedron is negatively charged, it is attracted to cations
Tetrahedra may link together by a cation (e.g. Mg, Fe, Na, Ca, K) serving as a bridge, or
Tetrahedra may link together by sharing oxygens
Isolated tetrahedral structure
Cations serve as links between tetrahedra; no sharing of oxygens
e.g. olivine, and garnet, which also happen to be mafic silicates
Single chain silicates
Adjacent tetrahedra form a chain by sharing 2 of their oxygens with neighboring tetrahedra
e.g. pyroxenes, which also happen to be mafic silicates
Double chain silicates
Two chains can link up by sharing oxygens
e.g. amphiboles, which are mafic silicates too
Sheet silicates
Sheets are formed when each tetrahedron shares 3 of its oxygens with its neighbors
e.g. micas, biotite (mafic) and muscovite (non-mafic), and clay minerals, which are non-mafic silicates
Framework silicates
Every oxygen in each tetrahedron is shared to form 3-D framework
e.g. feldspar, quartz, which are also non-mafic
Common non-silicate minerals
Calcite -- calcium carbonate -- Limestone is made of calcite.
Dolomite -- calcium magnesium carbonate
Gypsum -- calcium sulfate
Galena -- lead sulfide
Pyrite -- iron sulfide
Halite -- sodium chloride (table salt)
How to Identify Minerals: Physical Properties
Geologists determine the identity of an unknown mineral by describing its physical properties. They then use a reference book to find out what mineral has those properties. We will learn to describe the physical properties.
1. Habit refers to the overall shape of the mineral
use terms like: "equant" (3 dimensions of the mineral have about the same length, like a cube or sphere),
“elongate" (one direction is long but the other 2 are short, like a pencil), or "platy" (one dimension is short, other 2 are long like a sheet of paper)
isolated tetrahedra & framework silicate minerals tend to be equant in habit; chain silicates tend to be elongate, sheet silicates are platy
2. Cleavage
Refers to very smooth, flat, shiny breakage surfaces
These special breakage surfaces correspond to zones of weak bonding in the crystal structure
To describe cleavage, must determine the number of unique cleavage planes (directions) and their angle with respect to each other (e.g. salt breaks into cubes, with cleavage in 3 directions, all at 90 degrees)
3. Hardness
Refers to "scratchability" of the minerals harder minerals will scratch softer minerals
Rank minerals according to hardness using the Moh's scale
Fingernails are about 2.5 on Moh's scale; glass or steel knife is about 5.5; use these common items to estimate hardness of a mineral.
4. Color
Varies in many minerals, e.g. quartz
Some minerals come in just one color; other are many colors/many varieties
5. Streak
Refers to color of mark left by rubbing mineral against a streak plate (unglazed porcelain) streak does not vary even if color does.
6. Other Properties
Some minerals are magnetic
Some minerals effervesce ("fizz") in dilute acid
Specific gravity (like density)
Moh's Hardness Scale (Commit this to memory)
1.0            TALC
2.0          GYPSUM
FINGERNAIL
3.0          CALCITE
3.5          COPPER PENNY
4.0          FLUORITE
5.0          APATITE
5.5          STEEL KNIFE BLADE/GLASS PLATE
6.0          ORTHOCLASE FELDSPAR
7.0          QUARTZ
8.0          TOPAZ
9.0          CORUNDUM (RUBY)
DIAMOND

4. Crystal structure
Crystal structure depends on sizes of and charges on ions
Most common mineral group is the silicates
All silicate minerals contain silicon and oxygen
1. Mafic silicate minerals contain iron or magnesium and are dark in color.
Examples: olivine, pyroxene, amphibole, and biotite mica
2. Felsic silicates don't contain magnesium or iron, and are light in color.
Examples: feldspar, quartz, clay minerals, muscovite mica

5. Mafic silicate
Felsic silicate

6. Common non-silicate minerals
Fluorite – used as a toothpaste additive
Calcite -- calcium carbonate -- Limestone is made of calcite.
Dolomite -- calcium magnesium carbonate
Gypsum -- calcium sulfate
Galena -- lead sulfide
Pyrite -- iron sulfide
Halite -- sodium chloride (table salt)

8. How to Identify Minerals: Physical Properties
Geologists determine the identity of an unknown mineral by describing its physical properties. They then use a reference book to find out what mineral has those properties. We will learn to describe the physical properties.
Luster refers to the light reflected off of the mineral and its overall quality. Minerals can be termed: glassy, opaque, transparent, shiny, or most commonly: metallic and non-metallic.
One of the first determinations a geologist must make is whether the mineral in metallic or non-metallic.

9. Non-metallic mineral
Metallic mineral

10. Cleavage Refers to very smooth, flat, shiny breakage surfaces
These special breakage surfaces correspond to zones of weak bonding in the crystal structure.
To describe cleavage, one must determine the number of unique cleavage planes (directions) and their angle with respect to each other (e.g. salt breaks into cubes, with cleavage in 3 directions, all at 90 degrees)
NO cleavage

11. Hardness
Refers to "scratchability" or resistance to being scratched. Harder minerals will scratch softer minerals.
Geologists rank minerals according to hardness using the Moh's scale
Moh's Hardness Scale (Commit this to memory)
1.0     TALC
2.0    GYPSUM
FINGERNAIL
3.0    CALCITE
3.5    COPPER PENNY
4.0    FLUORITE (Note the spelling!)
5.0    APATITE
5.5    STEEL KNIFE BLADE/GLASS PLATE
6.0    ORTHOCLASE FELDSPAR
7.0    QUARTZ
8.0     TOPAZ
9.0     CORUNDUM (RUBY)
DIAMOND

12. Color
Varies in many minerals, e.g. quartz
VERY unreliable.
Some minerals come in just one color;
other are many colors/many varieties.
Streak
Refers to color of mark left by rubbing mineral against a streak plate (unglazed porcelain). Streak does not vary even if color does.
Other Properties
Some minerals are magnetic (i.e., magnetite)
Some minerals effervesce ("fizz") in dilute acid (calcite)
Specific gravity (like density) galena has a high specific gravity.

13. Key Terminology Mineral Chemical composition
Crystalline structure Ions
Cation Anion
Silicate Mafic
Felsic Silica tetrahedron
Single chain Double chain
Sheet silicate Framework silicate
Non-silicate Physical properties
Habit Luster
Streak Cleavage
Hardness Moh’s Hardness Scale