Chapter 3

Minerals Part II

How are Minerals formed?

• One way is the cooling of magma

• Atoms migrate together and form different compounds

• The elements present and the amounts determine the kind of minerals

How are minerals formed?

• Different crystal structures are formed at different temperatures

• If the magma cools slowly, large crystals are formed • Heavier minerals such as magnetite sink and lighter ones

float.

How are minerals formed?

• Minerals such as quartz and calcite form late in the cooling process and are known as hydrothermal minerals.

• In the last few years, hydrothermal vents have been formed on the ocean floor.

How are minerals formed?

• In these areas, sea water filters into the hot crust and is heated to 400 degrees C. The hot water then reacts with the crust and becomes a metal bearing liquid. When it returns to the cooler sea floor, it deposits minerals, including iron, copper and zinc sulfide.

Minerals from Solution

• When water is saturated with dissolved solids and can’t hold any more, the excess falls out of the solution.

• An example of this is the manganese nodules on the ocean floor

Minerals from Evaporation

• Minerals such as salt, gypsum and calcite (calcite forms in two ways) are formed from sea water when it evaporates.

• This happens in warmer parts of the world where the sun's heat evaporates the water and leaves the minerals.

Minerals from Weathering

• Chemical changes are caused by atmospheric oxygen, water and acid rain.

• Such action can change feldspars to kaolin and pyrite (fools gold) into a red-brown iron ore called iron pyrite (yellowboy)

Minerals from Metamorphosis

• Some minerals are formed when rocks are metamorphosed, that is subjected to heat and pressure

• Minerals formed in this way include garnet and mica.

Uses of Minerals

• Gems• Rarity and beauty makes

them valuable• Gemstones used for

jewelry are cut and polished and sometimes don’t resemble the raw form of the mineral

Gemstones

• May have a crystal structure that allows it to be cut in facetsMay have the addition of another mineral that gives it a brighter color

Ores

• A mineral is an ore if it contains a substance that can be sold for profit

• Hematite is the ore of iron • Bauxite is the ore of aluminum• Copper comes from chalcopyrite ore

Ores

Ores

• Ore deposits are formed when fluids travel through weaknesses in rocks, such as fractures and cracks.

• The minerals dissolved in the fluids are left behind when the liquid evaporates, forming “vein deposits”

Mining

• Ores are only profitable if the cost of mining them is less than the value of the material being mined

• Waste rock has to be removed • This can be expensive and harmful to the

environment