Rocks & Minerals

Minerals

• There are about 3000 known minerals• Minerals are made of elements (either a single

element or a combination of elements)• Examples of Minerals

– Gold: a mineral made of one element (gold…Au)

– Calcite: a mineral made of 3 elements (calcium, carbon, and oxygen…CaCO3)

gold calcite

• Must be naturally occurring (they must occur in nature)

• Must be inorganic (not made of living things)• Must be crystalline (have a crystal structure)• Must be solid (minerals are not gases and liquids)• Must have definite physical and chemical properties

Scientific Requirements for a Substance to be a Mineral

How do we identify minerals?

• By color: a red mineral is most likely not gold (which is a shiny gold color) or biotite (which is a black color)

• By luster: the luster of a mineral describes how shiny it looks (silver has a metallic luster and pure quartz has a glassy luster)

• By streak color: What color is the streak when a mineral is rubbed on a porcelain plate?

• By hardness: How hard is the mineral? (The Mohs hardness scale uses numbers to describe hardness)

Mohs Mineral Hardness Scale1) Talc

2) Gypsum

3) Calcite

4) Flourite

5) Apatite

6) Feldspar

7) Quartz

8) Topaz

9) Corundum

10) Diamond

Softest

Hardest

1

2

3

4

5

6

7

8

9

10

Rocks

• Rocks are mixtures of minerals• Most rocks are composed of at least 2 minerals• Example of a rock:

– Granite: contains 75% feldspar, 20% quartz, and 5% mica

Classifying Rocks

• Rocks are classified by how they formed and what they’re made of

• There are 3 general classes of rocks

– Igneous Rocks…are formed when lava and magma crystallize to form solid rock

– Metamorphic Rocks…are formed when an existing rock is partially melted, squeezed, or both

– Sedimentary Rocks…are formed when sediments (sand clay, and silt) are compressed and become solid rock

Examples of Different Classes of Rocks

Igneous

Granite cooled very slowly Obsidian cooled very quickly

Examples of Different Classes of Rocks

Metamorphic

Gneiss has bands because it was folded and compressed

Examples of Different Classes of Rocks

Sedimentary

Sandstone is made of sand grains Shale is made of clay particles