Rocks and the Rock Cycle

Igneous, Sedimentary, and Metamorphic varieties

Where do all rocks come from?

• All rocks basically come from magma (molten rock from the earth’s interior, which provides the parent material for igneous, sedimentary, and metamorphic rocks)

• The only exception are rocks composed of organic material ( a certain variety of sedimentary and metamorphic rocks)

The Rock Cycle

The Rock Cycle

The Rock Cycle

How the rock cycle works

• Relatively all rocks start out as igneous rocks. • IGNEOUS ROCKS are formed from volcanism• When igneous rocks are weathered, deposited

elsewhere and then solidified, they are then classified as SEDIMENTARY ROCK (lithified sediment)

• If an Igneous rock or a Sedimentary rock somehow gets buried and undergoes an extensive change in temperature and/or pressure, the rock will then become metamorphosed, so classified as METAMORPHIC ROCK

Igneous Rock

• Rock formed when magma cools and hardens via volcanism

• Two types – intrusive igneous and extrusive• Intrusive – when magma doesn’t quite make it to

the surface, but crystallizes and cools below the surface

• Extrusive- magma that makes it to the surface, now lava, that crystallizes and cools above the surface

Some cool intrusive sites

Yosemite, CA

Devil’s Postpile (Mammoth, CA)

Some typical intrusive igneous rocks

Some Cool Extrusive Igneous Sites

• Obsidian dome (Mammoth, CA)

Not Cool extrusive

Structures Related to Igneous Rocks

• Batholith- a large mass of intrusive igneous rock, sometimes called a pluton (think Sierra Nevada)

A pretty cool dike

For tomorrow……

• We will talk about and look at various igneous compositions (What’s chemistry and viscosity got to do with it?)

• Also, we will start to examine Sedimentary and Metamorphic Rocks and Structures