Transcript 5.2 - Period F

5.2
Structure and Composition of Minerals
A. What is a Mineral?
Occurs Naturally
 Is a solid
 Has definite Chemical Composition
 Atoms are arranged in an orderly fashion
 Inorganic (Never alive)

There are nearly 4000 minerals
8 major elements make up 98.5% of
Earth’s Crust
 Most abundant elements are Oxygen and
Silicon
 They make up 90% of most earth
minerals

The 8:
Oxygen
 Silicon
 Aluminum
 Calcium

Sodium
 Iron
 Potassium
 Magnesium

B. How Minerals Form

1. Magma Process
◦ Atoms, ions and molecules move freely in
magma
◦ As magma cools, different atoms bond
together to form minerals
◦ Cooling speed determines crystal size
 Fast = Small crystals
 Slowly = Larger Crystals
2. Pressure Process
Rocks (containing
minerals) are
subjected to high
temperature and
pressure
 Minerals break down
chemically
 Re-form into other
minerals

3. Evaporation Process

If a solution contains dissolved ions,
solution may evaporate and leave minerals
behind
Ex: Halite (NaCl – sodium chloride – salt)
Evaporating salted water will leave behind salt
crystals
C. Structure of Minerals
Arrangement of atoms determines the
shape
 Angle at which crystal faces meet helps
identify the mineral
 Six basic shapes- crystallographic axes are
used to distinguish between them.
 Axes pass through crystal center

1. Cubic System
3 axes of equal length
 Intersect at 90 degree angles

Galena
Pyrite
2. Orthorhombic System
3 axes of different lengths
 Intersect at 90 degree angles

Aragonite
3. Tetragonal System
3 axes, 2 of which are equal
 Intersect at 90 degree angles

Zircon
4. Triclinic System
3 axes, different lengths
 Intersect at oblique angles

Amazonite
5. Hexagonal System
4 axes, equal length
 Intersect at 60 degree angles

Beryl
6. Monoclinic System
3 axes of different lengths
 2 intersect at 90 degrees, third at oblique
angle

Selenite
D. Silicates
Include oxygen and silicon
 Can also include one or more metallic
elements
 90% of earth’s crust materials are silicates

Silica Tetrahedron
Basic structure of
silicates
 4 oxygen atoms
around a silicon
atom
 Can be arranged in
different ways
 Makes different
silicates

E. Crystal Structure and Physical
Properties
 Minerals
are solid
 Their atoms are tightly packed
 This means that there are strong
chemical bonds
Adding Heat
An increase in temperature can weaken
those bonds
 Minerals can melt, and even vaporize into
a gas if hot enough
 Can re-form into other minerals

Cleavage

The tendency for a
mineral to split along
a definite plane
Mineral Hardness
Depends on atomic arrangement
 Example: Carbon

◦ Tetrahedral formation makes diamond
◦ Hexagonal Sheet formation makes graphite
◦ Both made of carbon atoms
=
5.3 IDENTIFYING
MINERALS
1. Rock Forming Minerals
Mostly silicates
 Quartz, feldspar, mica, calcite
 Rocks are usually made from many of
these
 Rocks are often sampled to identify
minerals

2. Identifying Minerals by Inspection

Color
◦ Least useful

Luster
◦ The way it shines
◦ Metallic, greasy, oily, dull, earthy
3. Testing Mineral Specimens

Streak
◦ The color of a mineral’s powder
◦ Mark it makes on a ceramic plate

Cleavage
◦ Splitting along a surface
◦ Can happen in different directions

Fracture
◦ When minerals break along surfaces other
than cleavage

Hardness
◦ Resistance to being scratched
◦ Mohs Scale 1-10
 1 –softest 10- hardest

Specific Gravity
◦ Ratio of mineral’s mass to an equal volume of
water
◦ Measures density in relation to water

Chemical Test
◦ Some minerals react to hydrochloric acid
◦ Fizzes and releases Carbon Dioxide
4. Special properties of minerals

Double refraction
◦ Splits light rays

Fluorescence
◦ Glows under ultraviolet light

Phosphorescence
◦ Glows after UV light turned off

Radioactivity
◦ Releases subatomic particles
5.4 MINERAL GROUPS
Silicates

Quartz
◦
◦
◦
◦
◦
◦
Silica tetrahedra
Glassy/greasy luster
Hardness of 7
Industrial uses (watches, glass, lenses etc.)
Many colors
Found in many types of rocks

Feldspars
◦
◦
◦
◦
◦
◦
◦
2 cleavage directions
Pearly
Hardness of 6
Metals included in tetrahedra
2 groups: Potassium and Sodium-calcium
Used in glass and ceramics
Found in many rocks

Other Silicates
◦ Pyroxene Family
 All contain iron and magnesium
 Always dark in color
◦ Mica Family
 Soft silicates
 Perfect cleavage
 Brown or White

Amphibole
◦
◦
◦
◦
Complex minerals
Needle-like crystals
Found in igneous and metamorphic rocks
Shiny dark green, brown or black

Olivine
◦ Green
◦ Gem quality makes Peridot

Kaolinite
◦ Clay for china
◦ Paints
◦ Fiberglass
Carbonates

Combo of neg carbonate ions bonded to
pos metal ions
◦ Calcite
◦ Dolomite
Oxides and Sulfides
Lots of Iron
 Oxide – iron combined with oxygen
 Sulfide – iron combined with Sulfur

◦ Hematite – most common, red
◦ Magnetite – black iron, magnetic
◦ Pyrite – fool’s gold, sulfide