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Igneous Rocks

Igneous Rocks Rocks formed through the cooling and crystallization of molten rock; the starting point of the rock cycle
Magma Molten rock beneath the surface; hotter than the surrounding rock and has lower density and migrates upward through bedrock.
Lava Magma erupted at the surface; hot enough to melt.
Felsic Rocks >65% Silica (Si); Abundant in Sodium, Potassium, and Aluminum; Has little calcium, Iron, and Magnesium.
Mafic Rocks <52% Silica (Si); Abundant in Calcium, Iron and Magnesium; Has little Sodium, Potassium and Aluminum.
Viscosity The resistance to flow; Water is low and maple syrup is high in this.
Composition High silica increases viscosity
Temperature increases, viscosity lowers
Pressure lowers, viscosity lowers
Dissolved Gases increases, viscosity lowers
Lava Flows low viscosity
Pyroclastic Materials high viscosity
Extrusive Igneous Rocks Formed by lava at the surface; tend to crystallize rapidly; small crystals form; AKA volcanic rocks
Intrusive Igneous Rocks Formed from magma that cools in the crust; tend to crystallize slowly; larger crystals form; AKA plutonic rocks
Igneous textures Based on the size of the mineral crystals
Aphanitic (I.T) Fine-grained crystals; fast cooling; crystal nucleation is greater than crystal growth
Phaneritic (I.T) Coarse-grained crystals; slow cooling; crystal nucleation is less than crystal growth
Porphyritic (I.T) Variable crystal size; Phenocrysts are larger crystals; Groundmass are finer crystals
Pyroclastic (V.T) Fragmental material; Volcanic ash and bombs; Tuffs and wielded tuffs
Glassy (V.T) No crystals - not a true mineral; Extremely rapidly cooling
Vesicular (V.T) Contains numerous small holes
Primary Minerals Quartz, K Feldspar, Plagioclase Feldspar, Biotite, Hornblende, Pyroxene, Olivine
Ultramafic Rocks Very low Silica Content <45%; Generally green or black; very high density
Mafic Rocks Low Silica content 45%-52%; Usually dark green, grey or black; high density
Intermediate Rocks Moderate Silica content 53%-65%; Wide range of colors; moderate density
Felsic Rocks High silica content >65%; light color; lower density
Bowen's Reaction Series Mafic, Intermediate and Felsic rocks can all arise from the same source magma; Higher melting Temp for the minerals higher on the list and lower melting T for minerals lower on the list; Translates to mineral stability
Discontinuous Series Contains ferromagnesium silicates
Continuous Series Contains only non-ferromagnesium silicates
Assimilation Country Rock- the surrounding rocks in which magma intrudes; Consumed/melted by magma
Crystal Settling/Fractional Crystallization Crystals form and sink to the bottom of the melt because they are more dense, specifically the minerals higher on the Bowen's Reaction Series settle first.
Magma Mixing Different magma may converge into one chamber and mix; mixing of mafic magma with felsic magma would create intermediate magma
Spreading Zones Cracks in the ocean floor where magma breaches and is quenched by ocean water
Subduction Zones Crust is partially melted as it subsides into the mantle; Ocean sediments and Silicon rich continental crust are incorporated into the melt, making the magma more felsic
Pyroclastic Flows Ash and lava fragments in the air, buoyantly supported by the vapor
Lahars Mix of water, mud, ash, and pyroclastic material
Hot Spots Regions where mantle plumes breach the crust (ocean or continental) and form deposits; Mafic rocks
Phreatic Eruptions Incredibly explosive eruptions that occur when rising magma reaches groundwater and vaporizes the water into steam quickly
Pluton Collective term for intrusive igneous bodies that may be tabular, cylindrical, or massive including: Dikes, sills, laccoliths, volcanic pipes, batholiths, and stocks
Concordant Plutons Boundaries parallel the layering of the host country rock
Discordant Plutons Boundaries cut across the host country rock
Dike Discordant tabular igneous body that cuts across the structure of adjacent rocks or massive rocks
Sill Tabular igneous body that parallels the structure of surrounding rocks
Laccolith A concordant igneous body that has a domed upper surface, a flat lower surface parallel to the surrounding rock and is fed by a dike at its thickest point
Volcanic Pipes The central portion of a volcano through which magma is transported
Volcanic Neck Vertical pipe-like intrusion that represents a former volcanic vent/pipe
Batholith Large, usually discordant plutonic mass that covers mroe than 100 square kilometers at the Earth surface, with no known base
Stock A plutonic mass that covers less than 100 square kilometers at the Earth surface, that is usually discordant but not always
Created by: FaithRaquel2015