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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
– composed of ferromagnesian mineralsolivine, pyroxene, and amphibole. These are
oceanic. The water cooled them quickly.
 Mafic
– composed of mostly quartz and feldspar.
These are continental, cooling on dry land.
 Felsic
Igneous Rock
– 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
 Aphamitic
Igneous Rocks: Vocabulary
 Vesicular
sponges.
– gassy when formed, the rocks look like
Igneous Rocks
Texture – Cooling Rate – Crystal Size – Description - Type
Vesicular -fastnone - 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
– 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
 Felsic
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