1. Structure and Formation of Minerals
4.2 Mineral Formation
Structure and Formation of Minerals

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

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

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

5. Magma cooling underground

6. 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

7. 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

8. Small minerals
Feldspar in the cracks

9. Large minerals
Large feldspar

10. Very large minerals

11. 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

12. 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

13. Halite: Rock Salt

15. 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

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

17. Quartz Vein

18. Gold bearing vein in brown

19. Vein with a fault