IGNEOUS ROCKS The main types of igneaous rocks 3.5 / 5 based on 4 ratings ? GeologyASAll boards Created by: Nuala McBrideCreated on: 22-11-11 19:53 SILICIC - GRANITE CRYSTAL GRAIN SIZE: Coarse TEXTURE: Porphyritic COLOUR: Dark Grey to Pink SILICA PERCENTAGE: >66% ENVIRONMENT OF FORMATION: Plutonic MINERAL COMPOSITION: Orthoclase Feldspar, some biotite and Muscovite Mica and Hornblende 1 of 10 SILICIC - GRANODIORITE CRYSTAL GRAIN SIZE: Coarse TEXTURE: Porphyritic COLOUR: Grey or White SILICA PERCENTAGE: >66% ENVIRONMENT OF FORMATION: Plutonic MINERAL COMPOSITION: Mainly plagioclase, minor orthoclase feldspar, hornblende and biotite. 2 of 10 SILICIC - RHYOLITE CRYSTAL GRAIN SIZE: Medium TEXTURE: Porphyritic COLOUR: Pale - Shades of Brown (may show flow banding) SILICA PERCENTAGE: >66% ENVIRONMENT OF FORMATION: Hypobyssal MINERAL COMPOSITION: Quartz, Plagioclase, Mica and Orthoclase 3 of 10 SILICIC - OBSIDIAN CRYSTAL GRAIN SIZE: Glassy TEXTURE: Equicrystaline COLOUR: Grey or Black SILICA PERCENTAGE: >66% ENVIRONMENT OF FORMATION: Extrusive MINERAL COMPOSITION: Quartz, and Feldspar 4 of 10 INTERMEDIATE - ANDESITE CRYSTAL GRAIN SIZE: Fine TEXTURE: Porphyritic COLOUR: Speckled Grey or Brown SILICA PERCENTAGE: 52% - 66% ENVIRONMENT OF FORMATION: Extrusive MINERAL COMPOSITION: Mainly composed of Plagioclase Feldspar 5 of 10 INTERMECIATE - DIORITE CRYSTAL GRAIN SIZE: Medium TEXTURE: Porphyritic COLOUR: Dark - Black + White or Pink + Green SILICA PERCENTAGE: 52% - 66% ENVIRONMENT OF FORMATION: Hypabyssal MINERAL COMPOSITION: Plagioclase feldspar and hornblende 6 of 10 MAFIC - BASALT CRYSTAL GRAIN SIZE: Fine TEXTURE: Equicrstaline COLOUR: Dark - may have vesicles SILICA PERCENTAGE: 45% - 52% ENVIRONMENT OF FORMATION: Extrusive MINERAL COMPOSITION: Quartz, Plagioclase, Coliate and Pyroxene 7 of 10 MAFIC - DOLERITE CRYSTAL GRAIN SIZE: Medium TEXTURE: Porphyritic COLOUR: Dark - Grey, Black or Green SILICA PERCENTAGE: 45% - 52% ENVIRONMENT OF FORMATION: Hypabyssal MINERAL COMPOSITION: Quartz, Feldspar and Plagioclase 8 of 10 MAFIC - GABBRO CRYSTAL GRAIN SIZE: Coarse TEXTURE: Porphyritic COLOUR: Dark - Black or Muddy Green SILICA PERCENTAGE: 45% - 52% ENVIRONMENT OF FORMATION: Plutonic MINERAL COMPOSITION: Plagioclase Feldspar and pyroxene 9 of 10 ULTRA-MAFIC - PERIDOTITE CRYSTAL GRAIN SIZE: Coarse TEXTURE: Equicrystaline COLOUR: Dark - Green SILICA PERCENTAGE: <45% ENVIRONMENT OF FORMATION: Plutonic MINERAL COMPOSITION: Olivine and pyroxene 10 of 10
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