1. 5.2 Structure and Composition of Minerals

2. A. What is a Mineral? Occurs Naturally Is a solid Has definite Chemical Composition Atoms are arranged in an orderly fashion Inorganic (Never alive)

3. There are nearly 4000 minerals

4. 8 major elements make up 98.5% of Earth’s Crust Most abundant elements are Oxygen and Silicon They make up 90% of most earth minerals

5. The 8: Oxygen Silicon Aluminum Calcium Sodium Iron Potassium Magnesium

6. B. How Minerals Form 1. Magma Process ◦ Atoms, ions and molecules move freely in magma ◦ As magma cools, different atoms bond together to form minerals ◦ Cooling speed determines crystal size  Fast = Small crystals  Slowly = Larger Crystals

7. 2. Pressure Process Rocks (containing minerals) are subjected to high temperature and pressure Minerals break down chemically Re-form into other minerals

8. 3. Evaporation Process If a solution contains dissolved ions, solution may evaporate and leave minerals behind Ex: Halite (NaCl – sodium chloride – salt) Evaporating salted water will leave behind salt crystals

9. C. Structure of Minerals Arrangement of atoms determines the shape Angle at which crystal faces meet helps identify the mineral Six basic shapes- crystallographic axes are used to distinguish between them. Axes pass through crystal center

10. 1. Cubic System 3 axes of equal length Intersect at 90 degree angles Galena Pyrite

11. 2. Orthorhombic System 3 axes of different lengths Intersect at 90 degree angles Aragonite

12. 3. Tetragonal System 3 axes, 2 of which are equal Intersect at 90 degree angles Zircon

13. 4. Triclinic System 3 axes, different lengths Intersect at oblique angles Amazonite

14. 5. Hexagonal System 4 axes, equal length Intersect at 60 degree angles Beryl

15. 6. Monoclinic System 3 axes of different lengths 2 intersect at 90 degrees, third at oblique angle Selenite

16. D. Silicates Include oxygen and silicon Can also include one or more metallic elements 90% of earth’s crust materials are silicates

17. Silica Tetrahedron Basic structure of silicates 4 oxygen atoms around a silicon atom Can be arranged in different ways Makes different silicates

18. E. Crystal Structure and Physical Properties Minerals are solid Their atoms are tightly packed This means that there are strong chemical bonds

19. Adding Heat An increase in temperature can weaken those bonds Minerals can melt, and even vaporize into a gas if hot enough Can re-form into other minerals

20. Cleavage The tendency for a mineral to split along a definite plane

21. Mineral Hardness Depends on atomic arrangement Example: Carbon ◦ Tetrahedral formation makes diamond ◦ Hexagonal Sheet formation makes graphite ◦ Both made of carbon atoms =

22. 5.3 IDENTIFYING MINERALS

23. 1. Rock Forming Minerals Mostly silicates Quartz, feldspar, mica, calcite Rocks are usually made from many of these Rocks are often sampled to identify minerals

24. 2. Identifying Minerals by Inspection Color ◦ Least useful Luster ◦ The way it shines ◦ Metallic, greasy, oily, dull, earthy

25. 3. Testing Mineral Specimens Streak ◦ The color of a mineral’s powder ◦ Mark it makes on a ceramic plate

26. Cleavage ◦ Splitting along a surface ◦ Can happen in different directions Fracture ◦ When minerals break along surfaces other than cleavage

27. Hardness ◦ Resistance to being scratched ◦ Mohs Scale 1-10  1 –softest 10- hardest

28. Specific Gravity ◦ Ratio of mineral’s mass to an equal volume of water ◦ Measures density in relation to water Chemical Test ◦ Some minerals react to hydrochloric acid ◦ Fizzes and releases Carbon Dioxide

29. 4. Special properties of minerals Double refraction ◦ Splits light rays

30. Fluorescence ◦ Glows under ultraviolet light

31. Phosphorescence ◦ Glows after UV light turned off

32. Radioactivity ◦ Releases subatomic particles

33. 5.4 MINERAL GROUPS

34. Silicates Quartz ◦ Silica tetrahedra ◦ Glassy/greasy luster ◦ Hardness of 7 ◦ Industrial uses (watches, glass, lenses etc.) ◦ Many colors ◦ Found in many types of rocks

35. Feldspars ◦ 2 cleavage directions ◦ Pearly ◦ Hardness of 6 ◦ Metals included in tetrahedra ◦ 2 groups: Potassium and Sodium-calcium ◦ Used in glass and ceramics ◦ Found in many rocks

36. Other Silicates ◦ Pyroxene Family  All contain iron and magnesium  Always dark in color ◦ Mica Family  Soft silicates  Perfect cleavage  Brown or White

37. Amphibole ◦ Complex minerals ◦ Needle-like crystals ◦ Found in igneous and metamorphic rocks ◦ Shiny dark green, brown or black

38. Olivine ◦ Green ◦ Gem quality makes Peridot Kaolinite ◦ Clay for china ◦ Paints ◦ Fiberglass

39. Carbonates Combo of neg carbonate ions bonded to pos metal ions ◦ Calcite ◦ Dolomite

40. Oxides and Sulfides Lots of Iron Oxide – iron combined with oxygen Sulfide – iron combined with Sulfur ◦ Hematite – most common, red ◦ Magnetite – black iron, magnetic ◦ Pyrite – fool’s gold, sulfide