1. Minerals
Ch. 4

2. I. What Is A Mineral? Intro.
There are around 3,000 minerals in Earth’s crust
These play an important role in rock formation and shaping Earth’s surface.
Importance in early human history?

3. Mineral Characteristics
Mineral: A naturally occurring, inorganic with a specific chemical composition and a definite crystalline structure.
Naturally Occurring and Inorganic
Minerals are found in nature, not made in a laboratory.
Inorganic means that minerals are not alive and were never alive.
Solids with Specific Composition
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.

4. Definite Crystalline Structure
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.

5. Minerals from Magma Magma: Molten material found beneath Earth’s
surface.
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.
Slow cooling = larger crystals

6. Minerals from Solution
If a solution becomes supersaturated with another substance, mineral crystals precipitate (drop) out of the solution
Sometimes, elements dissolve in supersaturated solutions and the liquid evaporates, leaving crystals behind.

7. Mineral Groups Silicates: Minerals containing oxygen and silicon
Make up 96% of the minerals found in the crust
Quartz, feldspar
Carbonates: Minerals composed of one or more metallic elements with the carbonate compound CO3.
Calcite, dolomite, rhodochrosite
Primary minerals found in rocks like limestone and marble
Oxides: Compounds of oxygen and a metal
a. Hematite and magnetite

8. Sulfide: Compounds of sulfur and at least one other element.
Pyrite
Sulfate: Composed of the sulfate compound (SO4)
Anhydrite
Halides: Made of chloride or fluoride, along with calcium, sodium, or potassium
Halite
Elemental
Made of only one element
Copper, silver, gold

9. II. Identifying Minerals
Mineral Identification
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.

10. Tests
Color
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.

11. Luster 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.

12. Texture Definition: How a mineral feels to the touch.
-Smooth, rough, ragged, greasy, soapy, or glassy.

13. Streak
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.

14. Hardness (pg. 86) 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.

16. Cleavage and Fracture
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.

17. Density and Specific Gravity
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.

18. Special Properties
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.

19. Mineral Uses: Ores: Useful substances that can be mined at a profit.
Minerals are only classified as ores if they are useful and have human value
Mines: Ores are removed from Earth’s crust by mining.
a. Underground Mining vs. Open-Pit Mining

20. Gems Rare, beautiful, and valuable minerals are known as gems.
The rarer the mineral, the more valuable it is.
Trace elements may alter the color of the mineral, making it worth more or less.
a. Amethyst is a more valuable form of quartz.