ROCKS MINERALS

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


Scientific Requirements for a
Substance to be a Mineral
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•
•
•
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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

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 Scale
1) Talc

Softest

2) Gypsum
3) Calcite

1

5

4) Flourite
5) Apatite

2

6) Feldspar

6

7) Quartz
8) Topaz

3
7

9) Corundum
10) Diamond

9

Hardest

4

8

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