Rocks

•Understand the Rock Cycle•Identify Characteristics of Igneous Rocks•Identify Characteristics of Sedimentary Rocks•Identify Characteristics of Metamorphic Rocks

What is a Rock?

Naturally-occurring mixtures of minerals, mineraloids (no crystals), or organic matter

What is the difference between a rock and a mineral?

• A rock is made up of one or more minerals.

• A mineral is a rock but a rock is not necessarily a mineral.

Three Types of Rocks

• Igneous rock: forms when magma/lava cools and hardens

• Sedimentary rock: forms when sediments are buried, compacted & cemented together

• Metamorphic rock: forms when existing rock is subjected to great heat & pressure over a long period of time

Once a rock is formed, does it stay the same rock forever?

• No-Rocks continue to change from one form to another.

• Rocks are continually changed by many processes, such as weathering, erosion, compaction, cementation, melting, and cooling

• Rocks can change to and from the three types

What is the process through which rocks change?

• The Rock Cycle—earth materials change back and forth among the different types of rocks

• The processes of melting, cooling, weathering and erosion, cementation and compaction, and heat and pressure.

• There is no set path a rock must follow

How are rocks redistributed?

• The core, mantle, & crust are one giant rock recycling machine

Igneous Rocks

• Ignis” = Latin for “fire”• Formed from the cooling of either

magma or lava• The most abundant type of rock• Classified according to their origin and

composition• Igneous Rocks come from

magma/lava cooling down.

Origin-Where the rock Forms

• Intrusive Rocks – form below the surface of the earth–Cooling magma–Usually has large crystals–Cool slowly taking as long as

hundreds of years.

Extrusive Rocks– Form at the earth’s surface–Cooling Lava–Usually have small to no crystals–Cool very quickly-even happening in

the air after a volcanic eruption.

Occasionally rocks will have both large and small crystals

• called porphyritic• Cools in two

stages-in the ground large crystals grew at the surface small crystals grew.

Granite- Intrusive or Extrusive? Why?

Obsidian- Intrusive or Extrusive? Why?

Gabbro- Intrusive or Extrusive? Why?

Pumice- Instrusive or Extrusive? Why?

Basalt-Intrusive or Extrusive? Why?

Composition

• Basaltic Igneous Rocks —made from lava/magma that is low in silica, rich in iron and magnesium. Rocks are dark-colored.

• Granitic Igneous Rocks—made from magma/lava high in silica and oxygen. Rocks are light-colored

• Andesitic Igneous Rocks—have a composition between basaltic and granitic.