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Minerals: The Building Blocks of Rocks
I. Definition
II. Formation
III. Properties
IV. Classification
I. Definition of a Mineral
A. naturally occurringCannot be human made
B. inorganicCannot contain organic material
C. orderly internal arrangement of atoms (solid)Crystalline structure
D. definite chemical compositionDefines the mineral (e.g. Fe2O3 = hematite, whereas Fe3O4 = magnetite)
I. Definition
II. Formation
III. Properties
IV. Classification
II. Formation of Minerals
A. Process called crystallization
B. Igneous1. Magma = large crystals (beneath surface)2. Lava = small crystals (above surface)
C. Solutions1. Precipitation- water evaporates leaving behind
salts (surface)2. Deposition- minerals are deposited from
hydrothermal systems (beneath surface- veins)
I. Definition
II. Formation
III. Properties
IV. Classification
A. Crystal Form (or shape):1. external expression of a mineral’s
internal atomic structure2. planar surfaces are called crystal faces3. angles between crystal faces are
constant for any particular mineral
Quartz Pyrite
III. Properties of Minerals
B. Cleavage:1. The tendency of a mineral to break
along planes of weakness2. Described by:
a. Number of planesb. Angles between adjacent planes
Do not confuse cleavage planes with crystal faces! Crystal faces are just on the surface and may not repeat when the mineral is broken.
constant for each mineral
}
• Cleavage (1 direction):
Example: mica
• Cleavage (2 directions):
orthoclase
amphibole
• Cleavage (3 directions):
halite
calcite
• Cleavage (4 directions):
fluorite
C. Fracture:1. Minerals that do not exhibit cleavage are said
to fracture2. Types
a. Conchoidal- smooth curve, bowl-shapedb. Hackly- sharp, jagged edgesc. Uneven- rough and irregulard. Fibrous- shows fibers or splinters
Conchoidal fracture (quartz)
Hackly fracture (copper)
Uneven fracture (limonite)
Fibrous fracture (chrysotile)
D. Luster:1. How a mineral surface reflects light2. Two major types:
a. Metallic lusterb. Non-metallic luster
Metallicexample
Non-metallicexample
E. Color:1. Most obvious, but often misleading2. Different colors result from impurities
Example:fluorite
F. Streak:1. Color of a mineral in powdered form2. Obtained by scratching a mineral on an
unglazed porcelain plate
Example:Hematite
G. Hardness:1. The resistance of a mineral to scratching2. Mohs Scale of Hardness
a. Developed by Friedrick Mohs, 1812b. relative scalec. consists of 10 minerals, ranked 1 (softest)
to 10 (hardest)
Mohs Hardness Scale
Hardest (10) – Diamond
Softest (1) – Talc
Common objects:
- Fingernail (2.5) - Copper penny (3.5) - Wire nail (4.5) - Glass (5.5) - Streak plate (6.5)
H. Density:1. mass of a mineral divided by volume of
the mineral2. metallic minerals tend to have higher
densities than non-metallic mineralsGalenaD=7.5
QuartzD=2.65
I. Distinctive properties:1. taste (halite tastes salty)
2. feel (talc feels soapy, graphite feels greasy)
3. smell (sulfur smells like rotten eggs)
4. magnetism (magnetite attracts a magnet)
5. double refraction (calcite when placed over printed material, letters appear doubled)
6. reaction with hydrochloric acid (calcite fizzes)
I. Definition
II. Formation
III. Properties
IV. Classification
III. Classification of Minerals
A. Classified based on chemical composition
B. Most minerals contain only eight elements
III. Classification of Minerals
A. Classified based on chemical composition
B. Most minerals contain only eight elements
C. Groups
C. Groups
1. Native elementsa. Natural element in pure formb. Examples:
1. Copper, Cu2. Gold, Au3. Silver, Ag
C. Groups
2. Halidesa. Formed from halogen ions (F-, Cl-, Br-, etc.)b. Examples:
1. Halite, NaCl2. Fluorite, CaF2
C. Groups
3. Sulfidesa. Formed from sulfur ion (S2-)b. Examples:
1. Galena, PbS2. Pyrite, FeS2 3. Cinnabar, HgS4. Sphalerite, ZnS
C. Groups
4. Oxidesa. Formed from oxygen ion (O2-)b. Examples:
1. Hematite, Fe2O3
2. Corundum, Al2O3
3. Chromite, FeCr2O4
C. Groups
5. Carbonatea. Formed from carbonate ion (CO3
2-)b. Examples:
1. Calcite, CaCO3
2. Magnesite, MgCO3
3. Rhodochrosite, MnCO3
C. Groups
6. Sulfatea. Formed from sulfate ion (SO4
2-)b. Examples:
1. Barite, BaSO4
2. Celestite, SrSO4
C. Groups
7. Silicatesa. Formed from silicate ion b. Most common rock-forming mineralsc. Most complex (have varying Si/O
ratios)d. Examples:
1. Quartz, SiO2
2. Enstatite, MgSiO3
3. Benitoite, BaTi(Si3O9)- California’s state mineral