Download Minerals

Minerals
Ch. 4
I. What Is A Mineral?
A. Intro.
1. There are around 3,000 minerals in Earth’s crust
a. These play an important role in rock formation and shaping
Earth’s surface.
2. Importance in early human history?
B. Mineral Characteristics
1. Mineral: A naturally occurring, inorganic with a specific
chemical composition and a definite crystalline
structure.
a. Naturally Occurring and Inorganic
i.
ii.
Minerals are found in nature, not made in a laboratory.
Inorganic means that minerals are not alive and were never alive.
b. Solids with Specific Composition
i.
ii.
Some minerals, like gold, silver, and copper, are made only of one
element.
Others, like quartz, are made of an arrangement of elements.
-The proportion of these elements are unique to the mineral.
c. Definite Crystalline Structure
i.
ii.
The atoms in minerals are arranged in regular geometric patterns
that are repeated again and again.
Crystal: If the mineral is allowed to grow in an unrestricted space, it
usually takes the shape of one of the six major crystalline systems.
C. Minerals from Magma
1. Magma: Molten material found beneath Earth’s
surface.
a. The type and amount of elements present in the magma help
determine which minerals will form, while the rate at which it
cools determines the size of the crystals.
i.
Slow cooling = larger crystals
D. Minerals from Solution
1. If a solution becomes supersaturated with another
substance, mineral crystals precipitate (drop) out of the
solution
2. Sometimes, elements dissolve in supersaturated
solutions and the liquid evaporates, leaving crystals
behind.
E. Mineral Groups
1. Silicates: Minerals containing oxygen and silicon
a. Make up 96% of the minerals found in the crust
i.
Quartz, feldspar
2. Carbonates: Minerals composed of one or more
metallic elements with the carbonate compound CO3.
a. Calcite, dolomite, rhodochrosite
b. Primary minerals found in rocks like limestone and marble
3. Oxides: Compounds of oxygen and a metal
a. Hematite and magnetite
4. Sulfide: Compounds of sulfur and at least one other
element.
a. Pyrite
5. Sulfate: Composed of the sulfate compound (SO4)
a. Anhydrite
6. Halides: Made of chloride or fluoride, along with
calcium, sodium, or potassium
a. Halite
7. Elemental
a. Made of only one element
b. Copper, silver, gold
II. Identifying Minerals
A. Mineral Identification
1. Geologists rely on simple tests based upon a mineral’s
physical and chemical properties.
a. It is usually best to use a combination of tests rather than just
one to identify minerals.
2. Tests
a. Color
i.
Color is sometimes caused by the presence of trace elements.
- This is generally the least reliable clue to a mineral’s identity.
• Ex: Purple amethyst is from ferric iron, orange citrine contains
iron hydrate, milky quartz is from gas bubbles.
b. Luster
i.
Definition: The way a mineral reflects from the light.
-Either metallic or nonmetallic
• Shiny metal-like surfaces have metallic luster
• Nonmetallic surfaces may be described as dull, pearly, waxy,
resinous, or silky.
-Differences are caused by differences in chemical compositions of
minerals.
c. Texture
i.
Definition: How a mineral feels to the touch.
-Smooth, rough, ragged, greasy, soapy, or glassy.
d. Streak
i.
A colored powdered streak left behind from rubbing a mineral
across an unglazed porcelain plate.
-A mineral’s streak may not match the mineral’s external color.
-A mineral’s streak rarely changes, even if its external colors vary.
• Streak for fluorite is always white, even though the mineral
can be green, purple, yellow, or blue.
-Can only be used for minerals softer than the porcelain plate.
e. Hardness (pg. 86)
i.
Definition: How easily a mineral can be scratched.
- The mineral’s hardness is compared to the hardness of 10 known
minerals ranging from talc to diamond.
• Any mineral with a greater hardness than another mineral will
scratch that softer mineral.
-Hardness is one of the most reliable tests of mineral identification.
f. Cleavage and Fracture
i.
Atomic arrangement determines how a mineral will break.
-A mineral that splits relatively easily and evenly along one or more
flat planes shows cleavage.
• Geologists count the number of cleaved planes and study the
angle/angles between them.
-Minerals that break with rough or jagged edges are said to have
fracture.
g. Density and Specific Gravity
i.
2 minerals of the same size usually weigh differently (they have
different densities)
- D = m/v (density = mass/volume)
- Reflects atomic weight and mineral structure.
• Most common measure of density by geologists is specific
gravity.
>>Ratio pf the weight of a substance to the weight of an
equal volume of water at 4C.
h. Special Properties
i.
Properties unique to a mineral may be used for identification.
- Calcite bends light in 2 directions (Double reflection)
- Calcite fizzes when in contact with HCl
- Magnetite is magnetic
- Sphalerite makes a rotten egg smell on a streak plate.
C. Mineral Uses:
1. Ores: Useful substances that can be mined at a profit.
2. Minerals are only classified as ores if they are useful
and have human value
3. Mines: Ores are removed from Earth’s crust by mining.
a. Underground Mining vs. Open-Pit Mining
D. Gems
1. Rare, beautiful, and valuable minerals are known as
gems.
a. The rarer the mineral, the more valuable it is.
2. Trace elements may alter the color of the mineral,
making it worth more or less.
a. Amethyst is a more valuable form of quartz.