Minerals
Composition of the Sun
What are Planets Made of?
• Same material as Sun
• Minus the elements that remain mostly in
gases
• We find this pattern in a certain class of
meteorites
Chondrites
The Earth’s Crust looks Very
Different
Composition of the Crust
Minerals are the Chemicals that
make up the Earth
• NATURALLY-OCCURRING
• INORGANIC
• CHEMICAL COMPOUNDS
• ABOUT 3000 KNOWN
• 200 COMMON
• 20 ROCK-FORMING
Atomic Bonding
1. Atoms Gain or Lose Electrons
2. Electrical Neutrality
• (+) and (-) Cancel Out
3. Bonding (Satisfy 1 & 2)
• Ionic (NaCl)
• Covalent (O2)
• Metallic (Cu, Al, Fe)
• Hydrogen (in water)
Ionic and Covalent Bonding
Metallic Bonding
Hydrogen Bonding
Summary of Bonding
• Ionic bonding holds rocks and minerals
together
• Covalent bonding holds people and other
organisms together
• Metallic bonding holds civilization together
• Hydrogen bonding gives water its heatretaining and solvent properties
4. Lattices
• Atoms in crystals form a repeating pattern
called a Lattice
5. Radicals
• Many minerals contain groups of atoms that
behave as single units
IDENTIFYING MINERALS
COLOR -Sometimes Distinctive
• Often Unreliable
• Affected By:
–
–
–
–
Chemical Impurities
Surface Coating
Grain Size
Weathering
IDENTIFYING MINERALS
(Continued)
We Need Properties Directly Linked to
Atomic Structure:
• Hardness
• Density
• Luster
• Cleavage
• Crystal Form
Hardness
• Resistance to
Scratching
• Directly related to
relative strength of
atomic bonds
• Scratch Test (Mohs)
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Talc
Gypsum
Calcite
Fluorite
Apatite
Feldspar
Quartz
Topaz
Corundum
Diamond:
Density
• Directly related to
masses of
component atoms
and their spacing
• Usually very
consistent
Ice:
0.92
Water:
1.00
Halite:
2.18
Quartz:
2.65
Pyrite, Hematite,
Magnetite:
5.0
Galena:
7.5
Gold:
19.3
Platinum:
21.4
Iridium:
22.4
(densest material on
Earth)
Luster
Metallic or Nonmetallic is the most important
distinction.
Cleavage
• Tendency to split along smooth planes
between atoms in crystal
• Thus directly related to atomic structure
• Related to Crystal Form
Crystal Form
• Takes Luck & Practice
• Well-formed crystals are uncommon
• Crystal Classification is somewhat subtle
IDENTIFYING MINERALS
Geologic Setting
Special Properties
• Taste, Magnetism, Etc.
Experience and Reading
Professional Methods
• Chemical Analysis
• X-Ray Studies
• Thin Section
MAJOR MINERAL SUITES
Elements
Metallic:Au, Ag, Cu
• Not Al, Pb, Zn, Fe, etc.
Nonmetallic: C - Diamond, Graphite
• Sulfur
Sulfides: Dense, Usually Metallic
Many Major Ores
• Major Cause
of Acid Rain
Halide: Halite
Carbonates
• Principal
Components of
limestone and
dolostone
• Storehouse for
CO2
Oxide: Hematite
Hydroxide: Bauxite
MOST IMPORTANT
MINERAL SUITE:
The Silicate Minerals
•
•
•
•
Si + O = 75% of Crust
Silicates make up 95% + of all Rocks
SiO4: -4 charge
Link Corner-To-Corner by Sharing Oxygen
atoms
Silica Structures
Inosilicates - Chains
Asbestos
Phyllosilicates - Sheets
Silicates
Tectosilicates - ThreeDimensional Networks
• Quartz
Feldspars
Quartz
Minerals in Granite
Making Sense of Crystals
Unit Cells
All repeating patterns can be described in terms
of repeating boxes (unit cells)
The problem in Crystallography is to reason
from the outward shape to the unit cell
Which Shape Makes Each Stack?
Stacking Cubes
Some shapes that result from
stacking cubes
Symmetry – the rules behind the shapes
The Crystal Classes