Rocks

Chapter 4-1

The Rock Cycle

The Rock CycleRock – mixture of minerals, glass or organic matter.

Granite: igneous rockMica

Plagioclase

Orthoclase

Horneblend

quartz

Rock CycleOlder rocks are recycled to make younger rocks.Various processes that alter the rocks;

MeltingTemperature and pressureWeathering, erosion and deposition

Three basic rock groups are formed:

Igneous – melting and cooling

Sedimentary – weathering, erosion and deposition

• Cementing and compacting

Metamorphic – temperature and pressure

Igneous Rocks

Formed from molten material in earth’s crust that emerges or remains in earth’s crust.

Magma – liquid rock UNDER crust

Lava – liquid rock ON crust

Causes of extreme heat in Earth

Pressure

Heat from earth’s interior

Radioactive elements

Two kinds of igneous rocks

Intrusive igneous rocks –

Cooled slowly

Texture – coarse grained - time for large crystal growth

Found in surface of earth after weathering

Pegmatite

Extremely large crystals

Long time for crystal growth

Intrusive sites

Gabbro

Plagioclase feldspar

Pyroxene

Diorite

Salt and pepper rock

Granite

Hornblende – black

White Plagioclase – white/gray

Extrusive Igneous Rocks

Cools near earth’s surface

Cools quickly

Texture – fine grained

Rhyolite

Feldspar

Quartz

Biotite mica

Fine texture

Basalt

Iron rich

Pyroxene

Plagioclase

Olivine

Fine texture

Quick cooled

Obsidian

Volcanic glass

Texture – glassy

SiO2

Conchoidal fracture

Pumice Frothy or Glassy threadsSilica basedGases emitted from lava at explosion cause strings that make threadsSo light it floats on water

Scoria

Large holes made by gas escaping from lava

Volcanic cinders

Lava rock

Basaltic – darker than pumice

Classification of Igneous Rocks

Igneous rock classified by composition

Basalt – dense, heavy, dark colored

- rich in Fe and Mg

- lava quick moving

- ocean bottoms

Granitic – light colored, lower density

- magma thick contains Si and O2

- continental plates

- contains great deal of gases (explosive)

Andesite Andesite – between basalt and granite

- violent eruptions

Igneous rocks can be classified by;

CompositionBasalt – ferromagnesium – Fe and Mg

Granite – potassium and silicates SiO2

Texture:Large crystalsSmall/no crystals

Place of cooling:Intrusiveextrusive

Textbook page 92answer in notebook

Self Check 1,2, 3, 4,

Applying skills