1. Chapter 3: Matter and Minerals (part II)

2. Minerals: the building blocks of rocks
Definition of a Mineral:
naturally occurring
inorganic
solid
characteristic crystalline structure
definite chemical composition

3. How do we identify minerals?
Physical properties:
Color
Luster
Hardness
Crystal shape
Cleavage
Specific gravity
Other

4. Physical Properties of Minerals
Color:
Most obvious, but often misleading
Different colors may result from impurities
Example:
Quartz

5. Physical Properties of Minerals
Color:
Streak – color of a mineral in powdered form
(used for metallic minerals)
Obtained by scratching a mineral on a piece of unglazed porcelain.
Example:
Hematite

6. Physical Properties of Minerals
Luster:
How a mineral surface reflects light
Two major types:
Metallic luster
Non-metallic luster
Metallic
example:
Galena
Non-metallic
example:
Orthoclase

7. Physical Properties of Minerals
Hardness:
How easy it is to scratch a mineral
Mohs Scale of Hardness
relative scale
consists of 10 minerals, ranked 1 (softest) to 10 (hardest)

8. Mohs Scale of Hardness 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)

9. Physical Properties of Minerals
Crystal shape (or form):
external expression of a mineral’s internal atomic structure
planar surfaces are called crystal faces
angles between crystal faces are constant for any particular mineral
Quartz
Pyrite

10. Physical Properties of Minerals
Cleavage vs. Fracture:
The way a mineral breaks
Cleavage: tendency of a mineral to break along planes of weakness
Minerals that do not exhibit cleavage are said to fracture
Do not confuse cleavage planes with crystal faces! Crystal faces are just on the surface and may not repeat when the mineral is broken.

11. Physical Properties of Minerals
Cleavage is described by:
Number of planes
Angles between adjacent planes
These are constant for a particular mineral

12. Physical Properties of Minerals
Cleavage (1 direction):
Example: mica

13. Physical Properties of Minerals
Cleavage (2 directions):
orthoclase
amphibole

14. Physical Properties of Minerals
Cleavage (3 directions):
halite
calcite

15. Physical Properties of Minerals
Cleavage (4 directions):
fluorite

16. Physical Properties of Minerals
Fracture:
minerals that do not exhibit cleavage are said to fracture
smooth, curved surfaces when minerals break in a glass-like manner: conchoidal fracture
Quartz

17. Physical Properties of Minerals
Specific gravity:
weight of a mineral divided by weight of an equal volume of water
metallic minerals tend to have higher specific gravity than non-metallic minerals
Galena
SG=7.5
Quartz
SG=2.67

18. Physical Properties of Minerals
Other properties:
reaction with hydrochloric acid (calcite fizzes)
taste (halite tastes salty)
feel (talc feels soapy, graphite feels greasy)
magnetism (magnetite attracts a magnet)

19. Mineral Groups Rock-forming minerals
~30 common minerals make up most rocks in Earth’s crust
Composed mainly of the 8 elements that make up over 98% of the crust

20. SILICATES Mineral Groups Common cations that bond with silica anions
Element Abundances
Silica
(SiO4)4-
SILICATES
Common cations that
bond with silica anions
All others: %

21. Mineral Groups Silicates (most abundant)
Non-silicates (~8% of Earth’s crust):
Oxides O2-
Carbonates (CO3)2-
Sulfides S2-
Sulfates (SO4)2-
Halides Cl-, F-, Br-
Native elements (single elements; e.g., Au)

22. Mineral Groups – Silicates
Tetrahedron
fundamental building block
4 oxygen ions surrounding a much smaller silicon ion
Silicon-oxygen
tetrahedron
(SiO4)4-

23. Mineral Groups – Silicates
Joining Silicate Structures
How tetrahedra may be linked:
independent tetrahedra
single chains
double chains
sheets
3-D framework

24. Mineral Groups – Silicates –

25. Mineral Groups – Silicates
Olivine Group
dark silicates (Fe-Mg)
 ferromagnesian
No cleavage

26. Mineral Groups – Silicates
Pyroxene Group
Ferromagnesian / dark silicates (Fe-Mg)
Augite
2-directions
of cleavage
(at nearly 90 degrees)

27. Mineral Groups – Silicates
Amphibole Group
Ferromagnesian / dark silicates (Ca, Fe-Mg)
Hornblende
2-directions
of cleavage
(not at 90 degrees)

28. Mineral Groups – Silicates
Mica Group and Clay Minerals
light silicates (K, Al)
 non-ferromagnesian
Muscovite
1-direction
of cleavage

29. Mineral Groups – Silicates
Feldspar Group
light silicates (K-Na-Ca, Al)
K-feldspar
Most common mineral group
Orthoclase
Plagioclase
2-directions
of cleavage
(at 90 degrees)
Ca/Na-feldspar

30. Mineral Groups – Silicates
Quartz
light silicates (pure SiO2)
no cleavage
(conchoidal fracture)
hard, resistant to weathering
Quartz

31. Mineral Groups Non-ferromagnesian Silicates (K, Na, Ca, Al)
Silicates (Fe, Mg)
Oxides
Carbonates
Sulfides/sulfates
Native elements