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Identifying Minerals Ch. 5 Sec. 3

Identifying Minerals Ch. 5 Sec. 3. How can we identify minerals? inspecting them visually performing simple tests. Identifying Minerals by Inspection. Which properties can be determined visually? color, luster, & crystal shape should be considered together

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Identifying Minerals Ch. 5 Sec. 3

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  1. Identifying Minerals Ch. 5 Sec. 3 • How can we identify minerals? • inspecting them visually • performing simple tests

  2. Identifying Minerals by Inspection • Which properties can be determined visually? • color, luster, & crystal shape • should be considered together • rarely identified by a single property

  3. Identifying Minerals by Inspection • color • easily observed • some minerals have distinctive colors • color is generally unreliable for ID • Why?

  4. Quartz (SiO2) exhibits a variety of colors. milky quartz citrine amethyst smoky quartz

  5. From:geology.csupomona.edu/alert/mineral/minerals.htm

  6. dull earthy Identifying Minerals by Inspection • What is luster? • the way a mineral’s surface reflects light • How can we describe a minerals luster? • metallic • nonmetallic

  7. Galena is a lead sulfide that displays metallic luster

  8. Pyrite is an iron sulfide that displays metallic luster

  9. Examples of Nonmetallic Luster fibrous waxy pearly silky dull greasy/oily earthy resinous adamantine vitreous/glassy

  10. Testing Mineral Samples • What is streak? • color of a mineral in its powdered form • streak color is always the same • even though specimen can vary in color ALWAYS place streak plate on a flat surface. Never hold it in your hand. It can break and cut you.

  11. Examples of Streak

  12. Testing Mineral Samples • What is cleavage? • tendency to break along planes of weak bonding • What type of surfaces are normally seen? • flat, shiny surfaces (1, 2, 3, 4, 6 common) Cleavage Plane Animation

  13. Examples of cleavage – fluorite, halite, and calcite

  14. Muscovite Mica – one plane of cleavage

  15. Testing Mineral Samples • What is fracture? • tendency to break unevenly along rough or curved surfaces conchoidal fracture

  16. Testing Mineral Samples • What is a mineral’s hardness? • the ease or difficulty with which the mineral can be scratched • What affects a mineral’s hardness? • internal arrangement of atoms • & bond strength

  17. Testing Mineral Samples Softest Steel file Hardest • How is the hardness of a mineral determined? • compare to a standard scale • Mohs scale of hardness • 1—talc (softest) • 10—diamond (hardest)

  18. Determining Mineral Hardness • use fingernail, copper penny, glass “scratch” plate, & steel file/plate • If the mineral: • scratches the item • it is harder than that item • is scratched by the item • it is softer than the item • tells you mineral’s approx hardness ~Ex. If the mineral scratches glass, but does not scratch steel (or is scratched BY steel), its hardness is between 5.5 & 6.5 on Mohs Scale

  19. Testing Mineral Samples • What is specific gravity/density? • specific gravity is the density (mass/volume) of the mineral compared with the density of water (= 1)

  20. Special Properties of Minerals • What is double refraction? • “seeing double”

  21. Special Properties of Minerals www.hometrainingtools.com en.wikipedia.org • What is fluorescence? • tendency to glow when placed under UV light (“black-light”) http://www.sterlinghill.org/Tour%20information.htm

  22. Special Properties of Minerals • Taste • halite  salty • Remember… donot taste anything in the laboratory! http://mineral.galleries.com/scripts/item.exe?LIST+Minerals+Halides+Halite

  23. Special Properties of Minerals • magnetism • What element would these minerals contain? • “lodestone” acts like magnet • magnetite attracted to magnet http://www.minerals.net/mineral/oxides/magnetit/magneti4.htm

  24. Special Properties of Minerals • radioactivity • give off subatomic particles

  25. Special Properties of Minerals • “acid test/ reaction with HCl” • carbonates react with dilute HCl & other acids • see fizzing/ bubbling • Why? • releasing CO2 gas

  26. Special Properties of Minerals • Is this sample calcite or dolomite? • How can you tell? • Where could you look if you’re not sure?

  27. Special Properties of Minerals • odor • sulfur • What does it smell like?

  28. O2 - Si4+ O2 - O2 - O2 - Minerals Groups Ch. 5 Sec. 4 • Major silicates • Make up 90+% of mineral in Earth’s crust • Which 2 elements are always in silicate minerals? • What does a silicate molecule look like?

  29. Silicate Mineral Examples Mica Feldspar Olivine Quartz Pyroxene

  30. Major Silicates • Quartz • Glassy or greasy luster, colorless/white/or variety of colors, conchoidal or irregular fracture, hardness = 7 • 2nd most abundant mineral in Earth’s crust milky quartz citrine amethyst smoky quartz

  31. Aluminum atoms (yellow) with nearby Sodium atoms (green) to balance charge Major Silicates • feldspars • have aluminum in addition to Si & O • other metals can include potassium, sodium, calcium • 2 major groups • potassium feldspars • sodium-calcium feldspars • most abundant mineral family in Earth’s crust

  32. Major Silicates • potassium feldspars • orthoclase • pink/salmon, cleavage 2 directions at 90°, most commonly found in granite

  33. Major Silicates • sodium-calcium feldspars • plagioclase (plag) • white to gray, cleavage 2 directions nearly 90°, striations/fine parallel lines

  34. Muscovite Major Silicates • other silicates • pyroxene family • mica family • amphibole minerals • olivine group • kaolinite

  35. Common Non-silicate Minerals • many have economic value • carbonates • calcite • dolomite • oxides • hematite • magnetite • sulfides • pyrite

  36. Common Non-silicate Minerals • carbonates • contain CO3 & metal ions • 2 most important • calcite • colorless or white, hardness = 3, 3 perfect cleavages at more than 90° (rhombohedra), bubbles with acid • dolomite • hardness 3.5-4, cleaves into rhombohedra, bubbles in acid only if powdered

  37. Common Non-silicate Minerals • oxides & sulfides • contain significant amounts of iron • usually combined with oxygen (oxide) or sulfur (sulfide) • economically important • Why?

  38. Common Non-silicate Minerals • oxides • hematite • usually red (or silvery/metallic), earthy luster, uneven fracture, red-brown streak, hardness 5-6 • magnetite • black iron oxide, attracted to a magnet, hardness 5.5-6.5 • sulfides • pyrite (“fool’s gold”) • pale brass to golden yellow, metallic, hardness ~6, 6- or 12-sided crystals

  39. Nonsilicate Mineral Examples Spinel (Oxide) Halite (Halide) Gypsum (Sulfate) Hematite (Oxide) Calcite (Carbonate) Pyrite (Sulfide) Galena (Sulfide)

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