Structure and Formation of Minerals 4.2 Mineral Formation Structure and Formation of Minerals

Learning Targets: Describe how melted rock produces minerals Describe how hot rock produces different minerals Explain how minerals form from solutions

Mineral Formation Minerals form by: Formation from Hot Material Formation from Solutions Formation from Hot Underground Water

Formation from Hot Material Magma is molten rock Molten = melted Underground Magma Above ground Lava Most magma never becomes lava, it cools underground

Magma cooling underground

Cooling of Magma When magma cools, it solidifies Cool  Solidify  Crystallize Rocks: mixture of minerals Magma can solidify in seconds or over millions of years Crystal is a pure mineral

Cooling of Magma Quick cooling = small crystals Atoms do not have time to arrange themselves Slow cooling = large crystals Atoms arrange and rearrange themselves until they are in the most stable positions

Small minerals Feldspar in the cracks

Large minerals Large feldspar

Very large minerals

Cooling of Magma Magma cools slowly; lava cools quickly Lava traps more gas as it cools Sometimes lava cools so quickly no crystalline structure can develop

Formations from Solutions Water in nature always contains some amount of minerals  it is a solution Hot water holds more minerals Minerals can precipitate out of solution Precipitate: water evaporates but minerals are left behind Salts are most common

Halite: Rock Salt

Minerals from Hot Underground Water Water deep below the surface can be very hot Hot water = more minerals As water moves up through cracks in rocks Water cools  minerals are deposited Hot water = minerals dissolve Cold water = minerals precipitate

Mineral Rich Water When water deposits minerals into cracks in existing rock, veins are formed

Quartz Vein

Gold bearing vein in brown

Vein with a fault