Physical Properties of Minerals
Naming Minerals
Color
• Glauconite (greek: glaucos = blue-green)
Other Properties, Uses
• Magnetite
Components
• Chromite
Places
• Muscovite (Moscow)
People
• Biotite
Chemicals (And Minerals) Are
Classified By Their Anions
For Example: Iron Compounds
Have Little in Common
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•
•
•
•
Fe: Gray, Metallic
FeCl2: Light Green, Water Soluble
FeSO4: Light Green, Water Soluble
FeCO3: Brown, Fizzes in Acid
FeS2: Dense, Brittle, Metallic, Cubic Crystals
On the Other Hand, Sulfides have
Many Properties in Common
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•
•
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FeS2
CuFeS2
PbS
ZnS2
All are Dense, Brittle, Metallic, have Cubic
Crystals
Identifying
Minerals
Identifying Minerals
Color -Sometimes Distinctive
• Often Unreliable
• Affected By:
–
–
–
–
Chemical Impurities
Surface Coating
Grain Size
Weathering
Identifying Minerals
(Continued)
Hardness
• Resistance to Scratching
• Directly related to relative strength of
atomic bonds
• Scratch Test (Mohs)
• Indentation Test (Knoop)
Common Errors due to:
• Weathering, ‘Chalk' marks
• Breaking vs. Scratching
Mohs vs. Knoop Scales
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Talc:
Gypsum, Fingernail:
Calcite, Penny:
Fluorite:
Apatite:
Feldspar, Glass:
Quartz:
Topaz:
Corundum:
Diamond:
very small
30
135
163
430
560
820
1340
2100
7000
Identifying Minerals
(Continued)
Density
• Directly related to masses of component
atoms and their spacing
• Usually very consistent
Density - gm/cm3
(weight relative to water )
• Air:
0.001
Wood - Balsa: 0.1, Pine: 0.5, Oak: 0.6-0.9
Gasoline: 0.7, Motor Oil: 0.9
Ice:
0.92
Water:
1.00
Sugar:
1.59
Halite:
2.18
Quartz:
2.65
Most Major Minerals: 2.6-3.0
Aluminum: 2.7
Density
• Pyrite, Hematite, Magnetite: 5.0
Galena:
7.5
Iron:
7.9
Copper:
9
Lead:
11.4
Mercury:
13.6
Uranium:
19
Gold:
19.3
Platinum:
21.4
Iridium: 22.4 (densest material on Earth)
Density is Extremely Consistent
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•
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NaCl
Mol Wt. = 22.99 (Na) + 35.45
(Cl) = 58.44
Cl: 8 at corners of unit cube
shared 8 ways. 8 x 1/8=1
Cl: 6 in centers of cube face
shared 2 ways, 6 x ½ = 3
4 Cl per unit cell
Na: 12 along edges shared 4
ways, 12 x ¼ = 3
Na: One in center of cell
4 Na per unit cell.
Density is Extremely Consistent
•
•
•
•
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•
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Mol. Wt of a unit cell of NaCl = 4 x
58.44 = 233.76
233.76 gm of NaCl = 6.02 x 1023
unit cells
One unit cell = 233.76 gm/ 6.02 x
1023 = 38.83 x 10-23 gm
Unit cell = .564 nm on a side
Unit cell volume = .1794 x10-27 m3
= 17.94 x10-23 cm3
Density = 38.83 x 10-23 gm/17.94
x10-23 cm3 = 2.164 gm/cm3
Textbook value: 2.16 gm/cm3
Identifying Minerals
(Continued)
Luster
• Metallic or Nonmetallic is the most
important distinction.
• Resinous, waxy, silky, etc. are selfexplanatory.
• Vitreous is often used for glassy luster.
Identifying Minerals
(Continued)
Cleavage
• Tendency to split along smooth planes
between atoms in crystal
• Thus directly related to atomic structure
• Related to Crystal Form
• Every cleavage face is a possible crystal face
• Not every crystal face is a cleavage face.
Quartz commonly forms crystals but lacks
cleavage.
Parting
•
•
•
•
Related to Cleavage
Occurs Along Specific Atomic Planes
Not Present in All Cases
Due to Impurities, Inclusions Along Atomic
Plane
• Common in Quartz, Magnetite
Identifying Minerals
(Continued)
Crystal Form
• Takes Luck & Practice
• Well-formed crystals are uncommon
• Crystal Classification is somewhat subtle
Fracture
• Conchoidal = Curving, smooth (Glass, etc.)
Identifying Minerals
(Continued)
Geologic Setting
• Some minerals occur in all geologic
settings: quartz, feldspar, pyrite
• Some minerals occur mostly in sedimentary
settings: calcite, dolomite
• Some minerals occur mostly in igneous
settings: olivine
• Some minerals occur mostly in
metamorphic settings: garnet, kyanite
Identifying Minerals
(Continued)
Special Properties
• Taste, Magnetism, Etc.
Experience And Reading
Professional Methods
• Chemical Analysis
• X-Ray Studies
• Thin Section
Diffraction
Diffraction
Geochemical Associations
Anions and Complex Anions