1
2
Earth Materials: Minerals
What is a mineral?
A substance must meet 5 requirements to be
classified as a mineral
• What is a mineral?
• Properties/characteristics of different types of minerals
• Mineral structures and bonding
• Major categories of minerals
• Importance and uses of minerals
3
4
Mineral Properties
Mineral Properties
Three general categories:
Optical
Some optical properties
Color
Streak
Physical
Chemical
Luster
Double refraction
Fluorescence
Transmission of light (transparent, translucent, or opaque)
1
6
5
Streak
Example: hematite
Fig 2.26 Understanding Earth
Minerals of various colors
Understanding Earth
7
Metallic luster:
gold and pyrite
Double refraction in a transparent piece of calcite
8
Non-metallic luster:
feldspar, mica, olivine, and
quartz
2
9
10
Mineral Properties
Some physical properties
Hardness
Density
Crystal shape
How it breaks: cleavage and fracture
Understanding Earth
11
12
Mineral Properties
How a mineral breaks:
Fracture
Cleavage
Crystal of galena (left) (lead sulfide)
Crystal of quartz (right) (silicon dioxide)
These minerals differ in color, luster, light transmission, crystal form,
hardness, cleavage, and streak.
- key observations for cleavage:
- number of directions
- angles between them
Fig 2.10 Understanding Earth
3
13
Conchoidal
fracture in obsidian
Fig 4.3 Understanding Earth
15
14
Cleavage of mica
into thin sheets
Fig 2.23 Understanding Earth
16
Cleavage in calcite
Fig 2.24 Understanding Earth
Fig 2.25 Understanding Earth
4
17
18
Mineral Properties
Chemical properties
Acid test
Salty taste
Mineral Properties
Many other chemical tests
Some other properties
Habit
M
Magnetism
ti
Absorbs water
Smell
Fig 2.22 Understanding Earth
barite rosettes
(barium sulfate)
needles of stibnite
(antimony sulfide)
Some
unusual
crystal
Habits
Geology 2nd ed.
ed
Chernicoff
botryoidal
malachite
(green) with
azurite (blue)
(hydrous copper
carbonates)
19
20
In-class exercise
Working in groups,
examine and describe the properties of each
mineral sample provided
stellate pyrite
(iron sulfide)
5
21
22
Mineral Properties
Chemical bonds - how multiple atoms are held together
Mineral Properties
ionic
Relationship to:
atomic composition
covalent
l t
atomic structure and bonding
metallic
other types of bonding
23
24
Carbon atom
Fig 2.2 Understanding Earth
Graphite and Diamond
Both are composed of carbon
but have very different
properties. Fig 2.15 Understanding Earth
6
25
26
Structure
of halite
(sodium
chloride salt)
Fig 2.16
Understanding Earth
Structures of
graphite (left) and
diamond (right)
-1
Geology 2nd ed. - Chernicoff
+1
Ionic bonds hold
together Cl -1 and Na +1
27
Regular arrangement of
atoms in galena (left)
28
Understanding Earth
Cube-shaped crystals
(below)
The structure of galena is essentially
the same as in halite. Therefore, both
grow and break to form cubes. Their
color and luster are different,
however, because they have different
compositions (and bonding).
Fig 2.10 Understanding Earth
7
29
30
Some major groups of minerals
Silicates
e.g. quartz, feldspar, mica, olivine
Non-silicates:
Carbonates
Oxides
Sulfides
Sulfates
Native elements
Halides
e.g. calcite
e.g. magnetite, hematite
e.g. pyrite, galena
e.g. gypsum
e.g. native gold, copper
e.g. halite
Silicon-oxygen tetrahedron
Fig 2.16 Understanding Earth
31
32
Mica is built from
numerous sheets.
This explains the single
direction of cleavage
found in micas.
individual
tetrahedra
single
i l
chains
Types of silicate
mineral structures
double
chains
sheets
Muscovite Mica
3-D
frameworks
Figs 2.17 and 2.18 Understanding Earth
Geology 2nd ed. - Chernicoff
8
33
Minerals as Constituents of Rocks
34
Importance of Minerals
• Almost all rocks are made of minerals!
• Aesthetic value
Minerals
in Granite
• Natural resource value
35
Aesthetic value
Native gold
A large cut diamond
Smithsonian
Smithsonian
36
Iron ores
Fig 22.10 Understanding Earth
9
37
A great deal of effort goes into obtaining key mineral resources
U.S. reliance on imported mineral resources
38
Fig 22.17 Understanding Earth
Open pit copper mine south of Tucson, Arizona
Fig 22.22 Understanding Earth
U.S. reliance on imported mineral resources
Fig 22.17 Understanding Earth
39
40
Some Online Resources
Mineral resources info. from the USGS
http://minerals.er.usgs.gov/ http://minerals.er.usgs.gov/minerals/
http://www.usgs.gov/science/science.php?term=745
WebMineral Minerals Database
http://www.webmineral.com/
MinDat Minerals Database
http://www mindat org/
http://www.mindat.org/
Smithsonian Gem & Mineral Collection
http://www.gimizu.de/sgmcol/
Smithsonian Department of Mineral Sciences
http://www.minerals.si.edu/
More rock and mineral links (some with lesson plans)
http://edtech.kennesaw.edu/web/rocks.html
http://www.dlese.org/dds/browse_su_0k.htm (Digital Library for Earth System Education)
10