Rocks and their Origins

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What Are Rocks?

• Rocks are mixtures of minerals cemented together.

– Small rocks are just fragments of larger rocks.• Petrologist – earth scientist that

specializes in studying rocks, their composition, and how they change.

• Rocks are classified into 3 groups.1. Igneous 2. Sedimentary 3. Metamorphic

Igneous Rock Classification• Igneous rocks are

made of different kinds of minerals.– Quartz, mica, feldspar,

and pyroxene.• Igneous rocks can be

identified by their texture.– Slower the magma

cools, larger the crystals, which creates a rougher texture.

– Faster the magma cools, the smaller the crystals, the finer and smoother the texture.

Sedimentary• Sediments – large to

very small particles of rock.

• Sedimentary rocks form by layers upon layers upon layers of sediments.– Each layer presses on

the layer under it.

• Sometimes sedimentary rocks form from the remains of living things.

Classifying Sedimentary Rocks

• There are two types of sedimentary rocks.

• Clastic– Formed by

fragments of rock (pebbles and gravel)

• Nonclastic– Formed by

deposition of layers of minerals.

• Metamorphic rock is rock that has been changed through pressure and heat.

• Minerals go through chemical changes at temperatures from 200 °C to 800 °C

Metamorphic Rocks

Granite Schist

Rock Cycle• Rocks go through a cycle which natural

processes slowly change from one kind of rock to another – rock cycle.