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Igneous Rocks - Coggle Diagram
Igneous Rocks
Types of Texture: Size and shape of crystals in a rock
Aphanitic: Fine- grained. crystals cannot be seen with unaided eye
Extrusive
cools quickly above ground
Microscopic crystals
Glassy: no crystals indicate very rapid cooling or quenching
Extrusive
Cools very fast above ground
no crystals
Porphyritic: Mixture of large phenocrysts in a fine-grained groundmass slow then rapid cooling
Intrusive & Extrusive
2 stage cooling/ cools slowly underground & then erupts and cools quickly above ground
Microscopic crystals & Phenocrysts
Vesicular: some bubbles present. indicates low levels of gas in the lava.
Extrusive
Phaneritic: coarse grained, all crystals can be seen with unaided eye
Intrusive
Cools slowly below ground
smaller crystals than 1 cm but still visible
Pyroclastic or Fundamental: fragments of rocks or minerals. Indicates an explosive eruption
Extrusive
Pegmatitic: Very coarse grained, crystals larger than 1 cm
Intrusive
Cools very slow below ground
Big crystals
Composition: based on % of silica
Intermediate: 52-66% silica or 16-45% mafic minerals Potassium Feldspar, Plagioclase Feldspar, Hornblende, Biotite
Viscosity: Moderate to High/ Explosivity: High infrequent lava flow
50/50 dark and light
temp: low
Mafic: 45-52% silica or 45-85% mafic minerals Hornblende, Plagioclase feldspar, pyroxene, Olivine
Viscosity: low / Explosivity/ thin runny
mainly dark
Temp: high
Felsic: 66%-76% silica or 0-15% mafic minerals
Muscovite, quartz, Potassium Feldspar, Hornblende, Biotite
Viscosity: high / Explosivity: high
mainly light colored
temp: very low
Ultramafic: 38-45% silica or >85% mafic minerals Plagioclase feldspar, pyroxene, Olivine
Viscosity: Very low / Explosivity: Very low found in mantle
Temp: very high
Mafic Color Index: ratio of light (felsic) to dark (mafic) colored minerals
Melting
Decompression Melting: Melting caused by the decrease in pressure
Divergent Boundaries/ mantle plumes
Melting by Conduction/Heat transfer; magma comes into contact with rocks that have lower melting points
mantle plumes form in lower mantle as it rises pressure decreases adding melt
convergent, divergent, mantle plumes
Flux-Induced Melting/Fluid-Induced Melting: water driven off subducting plate. lower melting, magma forms, heat from magma melts
Convergent Boundaries
Partial Melting- only some minerals melt quicker due to different melting points depends on mineral/ Some solid minerals and some minerals will have melted
Cooling History/ Magma/ Lava
Extrusive: cooled on the earth's surface after erupting from a volcano/ melted rock on earths surface lava/ rocks that form when lava solidifies
Bowens Reaction Series: shows differences in chemical composition corresponds to difference in the types of minerals within an igneous rock/ determined the order of minerals as temperature drops
Discontinuous- mineral is transformed into different mineral through chemical reactions
Continuous- Plagioclase feldspar goes from being rich in Ca to Na
Intrusive: cooled within the earth/ when magma solidifies/ melted rock within the earth magma
Magma/ Lava: phases
Solid Phases- crystals formed
Liquid Phase: mobile ions (Si,O,Ca,Fe,Mg,Al,K)
Gas Phase: gases dissolved in melt, water vapor, CO2, Sulfur Dioxide