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

2. 2.2 Minerals Definition of a Mineral 1. Naturally occurring
2. Solid substance
3. Orderly crystalline structure
4. Definite chemical composition
5. Generally considered inorganic
Minerals: Building blocks of rocks

3. 2.2 Minerals How Minerals Form 1. Crystallization from magma
2. Precipitation
3. Pressure and temperature
4. Hydrothermal solutions

4. Minerals Formed as a Result of Crystallization of Magma

5. 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

6. 2.2 Minerals Mineral Groups
 Can be classified based on their composition
1. Silicates
Silicon and oxygen combine to form a structure called the silicon-oxygen tetrahedron. This silicon-oxygen tetrahedron provides the framework of every silicate mineral.

7. The Silicon-Oxygen Tetrahedron

8. Silicon-Oxygen Chains, Sheets, and Three-Dimensional Networks

9. 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: %

10. 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)

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

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

13. Mineral Groups – Silicates –

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

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

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

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

18. 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

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

20. 2.2 Minerals Mineral Groups 2. Carbonates 3. Oxides
Minerals that contain the elements carbon, oxygen, and one or more other metallic elements
3. Oxides
Minerals that contain oxygen and one or more other elements, which are usually metals

21. 2.2 Minerals Mineral Groups 4. Sulfates and Sulfides 5. Halides
Minerals that contain the element sulfur
5. Halides
Minerals that contain a halogen ion plus one or more other elements
6. Native elements
Minerals that exist in relatively pure form

22. Sulfides

23. Native Copper

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

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

26. 2.3 Properties of Minerals
Color
2.3 Properties of Minerals
 Small amounts of different elements can give the same mineral different colors.

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

28. 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

29. 2.3 Properties of Minerals
Streak
2.3 Properties of Minerals
 Streak is the color of a mineral in its powdered form.

30. 2.3 Properties of Minerals
Luster
2.3 Properties of Minerals
 Luster is used to describe how light is reflected from the surface of a mineral.

31. 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

32. Pyrite (Fool’s Gold) Displays Metallic Luster.

33. 2.3 Properties of Minerals
Crystal Form
2.3 Properties of Minerals
 Crystal form is the visible expression of a mineral’s internal arrangement of atoms.

34. 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

35. Quartz Often Exhibits Good Crystal Form.

36. 2.3 Properties of Minerals
Hardness
2.3 Properties of Minerals
 Hardness is a measure of the resistance of a mineral to being scratched.
 Mohs scale consists of 10 minerals arranged from 10 (hardest) to 1 (softest).

37. 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)

38. Mohs Scale of Hardness

39. 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)

40. 2.3 Properties of Minerals
Cleavage
2.3 Properties of Minerals
 Cleavage is the tendency of a mineral to cleave, or break, along flat, even surfaces.

41. 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.

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

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

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

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

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

47. Mica Has Cleavage in One Direction

48. 2.3 Properties of Minerals
Fracture
2.3 Properties of Minerals
 Minerals that do not show cleavage when broken are said to fracture.
 Fracture—the uneven breakage of a mineral

49. Conchoidal Fracture

50. 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

51. 2.3 Properties of Minerals
Density
2.3 Properties of Minerals
 Density is a property of all matter that is the ratio of an object’s mass to its volume.

52. 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

53. 2.3 Properties of Minerals
Distinctive Properties of Minerals
2.3 Properties of Minerals
 Some minerals can be recognized by other distinctive properties.

54. 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)