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Igneous rocks (Grain Structures (PORPHYRITIC- contains phenocrysts which…
Igneous rocks
Grain Structures
PORPHYRITIC- contains phenocrysts which form first at higher temperatures, unrestricted
EUHEDRAL- well developed , formed first at higher temperatures
ANHEDRAL- poorly developed, formed at a later stage at lower temperatures
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Structures
PILLOW LAVA- ball shaped masses of volcanic rock which are formed by the eruption of lava in water. They average at 1m and are kidney bean shaped
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Intrusions
DYKE- discordant to country rock, few cms to kms
SILL- concordant, few cms to 100m
BATHOLITH/PLUTON- large intrusion, 100s of kms, aureole of metamorphisis
minerals
Silicic- Quartz, Orthoclase, Plagioclase, Muscovite
Mafic- Biotite, Hornblende, Augite, Olivine
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GRANITE- coarse grained, crystalline, phenocrysts of orthoclase, plagioclase, quartz, biotite
GABBRO- coarse grained, slow cooling, magma chamber, granular, olivine, augite, plagioclase, hornblende
DOLERITE- medium grained, moderately slow cooling, small and shallow intrusion, granular
BASALT- fine grained, rapid cooling, surface lava, granular