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

Mineral Properties 1.Color and Clarity -Color -Clarity -Transparent = see- through -Translucent = foggy -Opaque = can’t see through

Mineral Properties 2.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!

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

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 = Streak plate = 6.5

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

Mineral Properties 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 Crystal form Cleavage

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)

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?

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