Minerals: Building blocks of rocks

1. Minerals: Building blocks of rocks • By definition a mineral is • Naturally occurring • Inorganic • solid • Ordered internal crystal structure • Definite chemical composition • Rock • A solid aggregate of minerals

2. 4 ways minerals form • Crystallize from magma • Precipitate out of water • Form from other minerals because of changes in temp. and pres. • Form from hydrothermal solutions

3. Rock-forming minerals • Common minerals that make up most of the rocks of Earth’s crust • Composed mainly of the 8 elements that make up over 98% of the continental crust

4. Silicate group • Silicates • Comprise 96% of crust • Elements: Silicon-oxygen tetrahedron (SiO4) • Fundamental building block for all silicates • Four oxygen ions surrounding a much smaller silicon ion • Form: Crystallize from magma

5. Light (felsic) Quartz: SiO2 Feldspar: KAlSi3O8 Dark (mafic) Pyroxene: MgFeSiO3 Amphibole: Ca2MgFeSi8O22 Olivine: Mg2Fe2SiO4 Uses: Glass, circuit boards Silicate group

6. Carbonate group • Elements: CO3 • Form: Crystallize from seawater • Examples • Calcite: Ca CO3 • Dolomite: CaMg CO3 • Uses: Cement, fertilizer

7. Oxide group • Elements: O • Form: chemical weathering • Examples: • Hematite: Fe2O3 • Magnetite: Fe3O4 • Uses: iron ore, pigment

8. Sulfate group • Elements: SO4 • Form: crystallize from seawater • Examples • Gypsum CaSO4 • Uses: Wall board, plaster

9. Sulfide group • Elements: S • Form: crystallize from hot water associated with volcanoes • Examples • Pyrite: FeS2 • Galena: PbS • Uses: metal ores

10. Halide group • Elements: metal and nonmetal • Form: crystallize from seawater • Examples • Halite: NaCl • Fluorite: CaF2 • Uses: salt, steel-making, fertilizer

11. Native element group • Form: often from hot water associated with volcanoes • Examples & uses: • Gold: Au - circuits • Silver: Ag • Copper: Cu – wires • Diamond: C – cutting • Graphite: C – pencil, lubricant

12. Abundance of minerals in the Earth’s Crust

13. The physical properties of a mineral (color, luster, cleavage/fracture etc.) depend on: • 1) Chemical composition (what elements comprise a mineral) of the mineral and • 2) Internal Crystal structure (how elements are put together [bonded] within minerals)

14. Polymorphs • Minerals with the same composition but different crystalline structures • Ex: Diamond and graphite

15. Physical properties: Color • Generally unreliable for mineral identification • Often highly variable • Small amounts of different elements (impurities) can give the same mineral different colors

16. External shape can reflect regular internal geometry Mineral Structure: Due to repeating arrangement of atoms or ions Halite (NaCl)

17. Physical properties: Streak • Color of a mineral in its powdered form • More important for metallic minerals • While color of a mineral may vary from sample to sample streak color does not.

18. Physical properties: Luster • Appearance in reflected light • Metallic – looks like a metal not just shiny (gold or silver) • Nonmetallic – can look many ways so need subcategories • Subcategories are: Glassy, waxy, greasy, resinous, pearly, earthy, dull

19. Physical properties: Crystal form • External expression of a mineral’s internal structure • Shown only occasionally • Often not displayed due to competition for space and/or rapid cooling

20. Physical properties: Hardness • Resistance of a mineral to abrasion or scratching • All minerals are compared to a standard scale called the Moh’s scale of hardness (not linear scale)

21. Physical properties: Cleavage • Tendency to break along planes of weak bonding • Produces flat, shiny surfaces • Described by: • Number of planes • Angles between planes

22. Physical properties • Fracture • Absence of cleavage when a mineral is broken • Conchoidal fracture – looks like broken glass Conchoidal Fracture in quartz

23. Density • Ratio of the mass of a substance to its volume • A mineral’s density depends on the chemical composition (elements) and how closely they are packed (structure) • Most minerals are between 2-3 grams/cm3 • When a mineral is very dense that can help to identify it. Examples: galena (PbS), Gold (Au) and Silver (Ag), uranium ores (U)

24. Special Properties • Magnetism • Reaction to hydrochloric acid • Malleability • Double refraction • Taste • Smell • Elasticity

25. Isotopes • Isotopes - atoms of the same element that differ in the number of neutrons they contain • Radioactive Isotopes – isotopes with unstable nuclei that break down at a constant rate over time • Half life – time it takes for half of the atoms to decay to the daughter product • Used to date rocks and fossils

26. The 8 Most Common Elements in the CRUST of the Earth (not whole earth) Write in the chemical symbol for each element • Silicon = • Oxygen = • Aluminum= • Iron= • Calcium= • Sodium= • Potassium= • Magnesium= What % do Si and O make up combined?

27. All minerals by definition have an internal crystal structure Type of structure is determined by the size relationship of the ions Mineral Structure

28. Density Lab vocabulary • Matter – anything that takes up space and has mass • Mass-the amount of matter in a substance • Weight – the force of gravity acting on the mass of an object • Volume – the amount of space an object takes up

29. Abundance of minerals in the Earth’s Crust