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Lab 4 - Minerals

Lab 4 - Minerals. Minerals 1. Inorganic 2. Naturally occurring Have characteristic chemical composition - Crystalline structure (orderly 3D arrangement of atoms/molecules) Rocks - Aggregates of 1+ mineral(s). Mineral Properties. Color and Clarity Color Clarity

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Lab 4 - Minerals

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  1. Lab 4 - Minerals • Minerals 1. Inorganic 2. Naturally occurring • Have characteristic chemical composition - Crystalline structure (orderly 3D arrangement of atoms/molecules) • Rocks - Aggregates of 1+ mineral(s)

  2. Mineral Properties • Color and Clarity • Color • Clarity • Transparent = see-through • Translucent = foggy • Opaque = can’t see through

  3. Mineral Properties • Crystal Form (Habit) • Geometric shape of the crystal • Cubes, pyramids, prisms, etc. • Perfect crystal habit = only occurs when crystal has room to grow (rare) • Different from cleavage  way the crystal grows, not the way it breaks!

  4. Mineral Properties 3. Luster • How light reflects off an object • Types: • Metallic luster (M) • Non-metallic luster (NM) • Vitreous • Waxy • Pearly • Satiny • Earthy • Greasy • Porcelaneous

  5. Mineral Properties 4. Hardness • Measure of mineral’s resistance to scratching. • Mohs Scale of Hardness • Quantitative scale of relative mineral hardness • 1 = talc (softest mineral) • 10 = diamond (hardest mineral) • Hardness of common objects: • Fingernail = 2.5 • Penny = 3.5 • Nail = 4.5 • Glass = 5.5-6 • Streak plate = 6.5

  6. Mineral Properties 5. Streak • Streak = the powder that remains when you scratch something against the streak plate • Minerals harder than 6.5 do not leave their streak • powder left behind = powder of streak plate • Usually same for the same mineral  even with different varieties of that mineral

  7. Mineral Properties Crystal form 6. Cleavage and Fractures • Cleavage = breaks along flat, parallel surface • Cleavage planes = parallel surfaces of weak chemical bonding • May be one or more • Cleavage direction = orientation of each set of cleavage plane • Fracture= break in a mineral not along a cleavage plane Cleavage

  8. Mineral Properties 6. Cleavage and Fractures • Cleavage direction may be: • Excellent, Good, Poor • Types: • Basal (mica) • Cubic (halite) • Octahedral (fluorite) • Dodecahedral (garnet) • Rhombohedral (calcite) • Prismatic • Conchoidal – ribbed, smoothly curved surfaces (like glass)

  9. Mineral Properties 7. Other properties • Reaction to acid – mineral fizzes when weak HCl is added • Carbonate minerals • Striations – straight, hairline grooves on the cleavage surface. • Feldspars • Magnetism – attracted to magnets • Specific gravity – ratio of the density of a substance divided by the density of water • How heavy is it?

  10. Notes on today’s lab • BEWARE OF COLOR! • The same mineral can be many different colors • Different minerals can be the same color • Identify consistently • Only write what you can see, don’t copy the book’s descriptions • 16 minerals, multiples for some • Minerals you will identify are all on your lab handout

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