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CH. 3
Rocks and Their
Origins
3-1 What are Rocks?
Rocks  mixture of minerals usually
cemented together
 Petrologist  scientist who studies
rocks and minerals and their origins
 There are 3 classes of rocks:

Igneous
Sedimentary
Metamorphic
3-2 How are Igneous Rocks Formed?
Igneous means “formed by fire”
 Igneous rocks  formed from magma
 Magma  molten rock under ground
 Lava  molten rock above ground
 Pluton  large bodies of igneous rock
formed when magma cools inside the
Earth

3-3 How are Igneous Rocks
Classified?

There are 6 common minerals that make
up igneous rocks: quartz, mica, amphibole,
feldspar, olivine, and pyroxene



Magma = slow cooling = large crystals = course texture
Lava = fast cooling = small crystals = fine texture
Lava = very fast cooling = no crystals = glassy
3-4 How are Sedimentary Rocks
Formed?
Sediment  rock particles, sand, silt,
clay, pebbles carried by wind, H2O,
or ice
 Sedimentary rocks form from being
cemented or compacted

3-5 How are sedimentary rocks
classified?
Clastic sedimentary rocks  made
up of fragments of rocks
 Nonclastic sedimentary rocks 

Made up of dissolved minerals (chemical)
 Remains of plants and animals (organic)

3-6 How are Metamorphic Rocks
Formed?
Metamorphic rocks are “changed
over” rocks
 Metamorphic rocks form from preexisting rocks
 Heat and pressure causes chemical
change to a rock

3-7 How are Metamorphic Rocks
Classified?
Foliated metamorphic rocks 
minerals are arranged in bands and
break into layers
 Nonfoliated metamorphic rocks 
the minerals are not arranged in
bands and do not break in layers

3-8 What is the Rock Cycle?

Rock Cycle 
series of natural
processes where
a rock is slowly
changed into
another kind of
rock