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Igneous Rocks
Formed from cooling and crystallization of molten rock.
Plutonic Rocks
Intrusive rocks formed below Earth's surface.
Volcanic Rocks
Extrusive rocks formed on or near Earth's surface.
Magma Components
Includes melt, solids, and volatiles.
Cooling Rate
Influences crystal size in igneous rocks.
Coarse-Grained Texture
Larger crystals formed by slow cooling.
Fine-Grained Texture
Smaller crystals formed by rapid cooling.
Glassy Texture
Very rapid cooling produces no crystals.
Dark Silicates, lower % of SiO2
Mafic minerals are rich in magnesium and iron—lower K feldspar. More calcic plagioclase.
Light Silicates, greater % of SiO2
Felsic minerals are high in silica and potassium. More sodic plagioclasese.
SiO₂ Content
High SiO₂ indicates felsic minerals.
Geothermal Gradient
Temperature increases ~25°C per km depth.
Decompression Melting
Melting due to pressure reduction during ascent.
Volatiles in Melting
Water addition lowers melting temperature.
Bowen's Reaction Series
Minerals crystallize based on melting temperatures.
Magmatic Differentiation
Evolving magma composition as minerals crystallize.
Basaltic Magma
Common in oceanic settings like mid-ocean ridges.
Andesitic Magma
Typical in continental settings, intermediate composition.
Granite
Felsic rock, coarse-grained, high SiO₂ content.
Basalt
Mafic rock, fine-grained, low SiO₂ content.
Obsidian
Glassy igneous rock formed from very rapid cooling.
Phaneritic
course grained, visible minerals, intrusive.
Aphanitic
fine-grained, no naked eye crystals, extrusive.
Felsic
light silicates, non-ferromagnesian.
Mafic
Dark silicates, ferromagnesian
Upper athenosphere
rocks are close to melting
adiabatic cooling
process of reducing heat through change in air pressure caused by volume expantion.
Partial Melting
T and which rocks begin to melt.
Adiabatic rise
no conductive heat loss
Volatiles
dissolved gas in the melt
