Chapter 3, Section 2 Igneous Rocks Wednesday, December 2, 2009 Pages 78 -- 81.
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Transcript of Chapter 3, Section 2 Igneous Rocks Wednesday, December 2, 2009 Pages 78 -- 81.
Characteristics
• Igneous rocks are any rocks that form from magma or lava.– Comes from the latin word “fire”.
• Most igneous rocks made of mineral crystals.
• The are classified according to their origin, texture, and mineral composition.
Extrusive Rocks
• Formed from lava that is cooled above the surface.
• Most common is Basalt.– Basalt forms much
of the crust including the crust beneath the ocean floor.
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Intrusive Rocks
• Formed when magma hardened beneath the Earth’s surface.
• Granite is the most abundant.– Part of the Earth’s
crust that makes up the continents.
– Granite forms the core of many mountain ranges.
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Texture
• Depends on the size and shape of its mineral crystals.
• May be fine-grained, coarse-grained, glassy or porphyritic.– Rapid cooling forms fine-grained
rocks.– Slow cooling forms coarse-grained
rocks.
Porphyritic Texture
• A rock with large crystals scattered on a background of much smaller crystals.
• Formed when intrusive rocks are cooled in 2 stages.– Change in cooling rate
due to movement of the magma.
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Mineral Composition• Most of the Earth’s
minerals contain silica.– Material formed from
oxygen and silicon.– Amount of silica affects the
type of rock they form.– Low in silica: Dark-
colored rocks (Basalt)– High in silica: Light-
colored rocks (Granite)
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Basalt
Granite
Uses of Igneous Rocks
• Many igneous rocks are hard, dense, and durable.– Used for tools and
building materials
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