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gneous Rocks

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Molten rock cools mass of intergrown crystals and/or glass!

Crystalline/glassy textures!

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Magma! Below the earths surface molten rock

= magma Molten rock, dissolved gasses, growing

crystals (as the magma cools) Magma under pressure

Less dense than surrounding rocks Rises/squeezes into cooler crust*Magma pushing itself into crust =

Intrusion

Cools to form intrusive igneousrock (visible cr stals, coarse

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Magma Lava Magma approaches earths surface Decrease in pressure

Bubbles of carbon dioxide dissolvedgasses separate from magmaLava

Erupts onto Earths surfaceExtrusive Igneous Rock

Fine-grained, tiny crystals/glass

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Intrusions Batholiths massive, 100km^2 +,

small bodies amalgamate Sills sheet-like, in between layers of

bedrock Laccoliths smaller pools Pipes Feed volcanoes! Dikes cut across layers of bedrock

in sheets Ring dikes look circular from above Radial dikes come off of pipes

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Phaneritic

Pegmatitic

Aphanitic

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Other Textures Vesicular Texture bubble

trapped in cooling lava Pyroclastic Texture volcanic ash

to blocks Porphyritic Phenocrysts and

matrix Can indicate slow to fast cooling

Changes in magmacomposition/viscosity

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Minerals in Igneous Rocks Type and abundance of minerals 8 Rock-Forming Minerals

Quartz, potassium feldspar (K-spar),plagioclase feldspar, muscovitemica, biotite mica, amphibole,pyroxene and olivine.

Light colored felsic (feldspars,silica) Dark colored mafic (magnesium,

iron) Aka ferromagnesian

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Identification Process Steps 1 and 2: Color and Mineral

Composition Estimate the % of mafic minerals in

the rock Identify the minerals and estimate

their percent by volume within thewhole rock

Can use GeoTools Step 3: Texture

Intrusive? Extrustive? Phaneritic?Glassy?

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( )Rhyolite felsic

( )Pumice felsic

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Phonolite( )Intermediate

Diorite( )Intermediate

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( )Pyroxene Mafic

( )Chromite ultramafic

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Bowens Reaction Series Modeling how different kinds of

igneous rocks can differentiatefrom a single body of magma as itcools

Periodite Melt rocks at 1200-1400deg C

Allow it to cool Note the crystals forming at

each temperature Sudden cooling

Continuous crystallization

series and a discontinuous

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Composite Volcanoes(Stratovolcanoes)

Formed by alternating layers of molten rock and rock fragments

Usually conical, peak shaped Explosive eruptions

Viscous magma increases pressure

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. ,Mt Shasta CA

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Shield Volcanoes Generally expansive in size Lava spills out of vent(s) Low explosivity Characteristic by hotspots ring of

fire

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Todays Lab.. Use characteristics to ID 8 igneous

rock samples Answer questions pertaining to

photos in the lab book Answer questions concerning

volcanoes!

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1

2

3

What type of volcano isthis?

Give three pieces of!evidence

Describe a typical eruption.for this volcano

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