Rocks

Igneous, Metamorphic, Sedimentary

What is a Rock?

A rock is a mixture of minerals , mineraloids, glass and organic matter.

Common minerals found in rocks include: feldspar, hornblende, and mica.

Granite is a mixture of these minerals.

Rock Cycle

There are three types of rock: Igneous – formed by melting and cooling magma

and lava. Sedimentary – formed by weathering and erosion Metamorphic – formed by heat and pressure over

time. Rocks change over time.

Igneous Rocks

Molten or liquid material from a volcano or from deep inside the Earth, cools to form igneous rocks.

Magma – High temperatures and high pressure deep in the Earth cause rocks to melt and form hot magma.

Earth’s Interior

Earth’s Interior: Temperatures

Igneous Rocks

At 60 to 200 km below the Earth’s surface the temperatures reach 1400oC. (2550oF)

Magma rises because it is less dense than the surrounding solid rock.

Igneous Rocks

Lava is magma that reaches the surface.

Ropeypahoe

lava

Igneous Rock: Intrusive Rocks

These are igneous rocks that form below the Earth’s surface.

They have large mineral grains. Examples : Gabbro

Diorite

Igneous Rocks:Extrusive

These rocks are formed quickly when lava cools on or near the Earth’s surface.

Air and Moisture causes lava to cool quickly. The quick cooling does not allow large crystals to

form. Extrusive rocks have a fine-grained structure.

Igneous Rocks: Extrusive Examples

Rhyolite

Obsidian

Igneous Rocks: Extrusive Scoria - formed from gassy lava, it has air-pockets that give it a spongy appearance.

Pumice: Lava “foam”, some samples float in water.

Volcanoes

Pompeii, Italy Web

Igneous Rocks: Vocabulary Mafic – composed of ferromagnesian minerals-

olivine, pyroxene, and amphibole. These are oceanic. The water cooled them quickly.

Felsic – composed of mostly quartz and feldspar.These are continental, cooling on dry land.

Igneous Rock

Aphamitic – texture , made of crystals too small to be seen without a microscope.

Porphyritic – rocks with two cooling rates,

They have a mix of large and small crystals. Porphyritic = look like chocolate chips! cookies

Igneous Rocks: Vocabulary

Vesicular – gassy when formed, the rocks look like sponges.

Igneous Rocks Texture – Cooling Rate – Crystal Size – Description - Type

Vesicular -fast- none - air bubbles – extrusive Glassy – fast – none - very smooth – extrusive Aphanitic –quick–microscopic –fine grained - extrusive

Granitic – slow – visible – coarse grained - intrusive Porphoritic – slow/then quick – small&large – Chocolate

chip - Intrusive

Mineral Composition of Igneous Rocks

Name – Minerals – Color – Density- Crustal Formation

Felsic – K-Feldspar, muscovite, quartz – Light – Low density – Continental

Intermediate- Hornblende, biotite, Na-plagioclase – Medium – Medium density – Continental/Ocean

Mafic – Olivine, Augite, Ca-plagioclase – Dark – High density - Oceanic