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Igneous Rock Formation

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Presentation on theme: "Igneous Rock Formation"— Presentation transcript:

1 Igneous Rock Formation
Molten rock comes from depth (less dense so works its way to surface) - full of gases (H20, C02, S02) plus elements in silicates Eruption - gases escape as pressure lessons Magma cools and hardens beneath the surface (intrusive; plutonic) Crystallization - process of cooling and solidifying Lava cools and hardens on surface (extrusive) In volcanic eruptions on or under the earth’s surface

2 Intrusive Igneous Rocks
Form when magma hardens beneath Earth’s surface Coarse grained due to slow cooling Examples- Granite, Diorite, Gabbro, Periodotite (image on left is diorite)

3 Extrusive Igneous Rocks
Form when lava hardens above the Earth’s surface, when most of the gases have escaped Fine grained due to rapid cooling Examples- Basalt, Rhyolite, Scoria (image on right is basalt)

4 Classification of Igneous Rocks
Texture- size, shape, arrangement of crystals Composition- proportions of light and dark minerals in the rock (images from top to bottom: obsidian, diorite, basalt)

5 Coarse Grained = Large Crystals
Intrusive rocks Magma cools slowly Ions have time to move large distances within magma Few centers of crystal growth develop

6 Fine Grained: Fast Cooling
Extrusive rocks Magma or lava cools rapidly resulting in small, interconnected mineral grains The ions in the melted material lose their motion and quickly combine

7 Glassy Texture Fast Cooling, Extrusive
No time for the ions in the lava to arrange themselves into a network of crystals Obsidian (top); pumice (bottom)

8 Porphyritic Texture: Different Sized Crystals
Minerals that do not crystallize at the same rate or time in magma --different sized crystals Inside volcano some magma never reaches the surface--two waves of crystallization Large crystals called phenocrysts (visible-crystals) in a matrix of fine grained crystals

9 Granitic Composition 0%-25% dark Felsic Light colored Quartz, feldspar
10% dark silicate materials-- with magnesium, iron 70% silica (light silicates) Example- Rhyolite (also granite)

10 Basaltic Composition 45%-85% dark minerals Plagioclase feldspar
Rich in magnesium and iron Darker and denser (because of iron) Mafic Ocean floor = basalt Example- Basalt (also gabbro)

11 Andesitic Composition
Between granitic and basaltic 25%-45% ‘dark’ 25% dark silicate minerals-- amphibole, pyroxene, biotite mica Other dominant mineral: Plagioclase feldspar Example- Andesite (also diorite)

12 Ultramafic Composition
85%-100% dark Olivine and pyroxene Almost entirely dark silicate minerals Peridotite rock. Rare at E’s surface but composition of much of mantle


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