Download Classifying Rocks

Classifying Rocks
What are Rocks?
 Made of two or more different minerals
that have been:
• cemented together
• squeezed and heated together
• melted and cooled together.
Mineral Composition and Color
• About 20 minerals make up most of the rocks
of Earth’s Crust.
• These minerals are known as rock-forming
minerals.
Texture
• Very useful in identifying a rock
• Look and feel of the rock’s
surface
• Most rocks are made up of
particles of other rocks – called
grains
• Geologists use terms based on
the size, shape, and pattern of
the grains
Grain Size
• Coarse Grained – large easy to see
• Fine Grained -- grains are so small they can only
be seen under a microscope
Fine Grain
Coarse Grain
Grain Shape
• Grains in a rock vary widely in shape
• The grains can be round (Conglomerate), jagged
(Breccia), star-shaped, look like small seeds, etc…
• They can be formed from other rocks
Conglomerate
Breccia
Grain Pattern
• The grains in rocks often
form patterns.
– Flat layers like pancakes
– Swirling patterns
– Foliated – different
colored bands
– Random
How Rocks Form
• Using color, texture, and mineral composition,
geologists can classify rock according to its
origin.
Igneous rock – forms from cooling magma or lava
Sedimentary rock – forms when particles of other
rocks or the remains of plants and animals are
pressed and cemented together.
Metamorphic rock – forms when an existing rock is
changed by heat, pressure, or chemical reaction.
Classifying Rocks Review
•
•
•
•
•
•
•
Where do rocks come from?
What are Rocks?
Mineral Composition
Color
Texture
Grain – size, shape, pattern
How Rocks Form?
The End