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 Properties2. 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 Properties4. 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

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 Properties7. 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