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ROCKS under the microscope

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ROCKS under the microscope. The ROCKS you need to know granite diorite gabbro dolerite basalt shelly limestone sandstone arkose greywacke marble schist. biotite.

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ROCKS under the microscope

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  1. ROCKSunder the microscope

  2. The ROCKS you need to know • granite • diorite • gabbro • dolerite • basalt • shelly limestone • sandstone • arkose • greywacke • marble • schist

  3. biotite PPLXPLGraniteNote how light and clear it is under PPL and grey/white/black under XPL; main minerals – feldspars (often microcline), quartz, biotite and muscovite biotite muscovite plagioclase plagioclase muscovite quartz quartz

  4. amphibole amphibole biotite biotite plagioclase plagioclase PPLXPLDioriteDarker under PPL than granite with more coloured minerals; much plagioclase and amphibole/biotite, only small amount of quartz

  5. pyroxene pyroxene PPL XPLGabbroCoarse-grained; darker under PPL and brightly coloured under XPL; main minerals – plagioclase, pyroxene and olivine plagioclase plagioclase olivine olivine olivine

  6. PPL XPLDoleriteMedium-grained;darker under PPL and brightly coloured under XPL; main minerals – plagioclase (often in form of laths), pyroxene (intergrown through other crystals) and olivine plagioclase plagioclase pyroxene pyroxene

  7. fine groundmass of plagioclase & iron minerals PPL XPLBasaltFine-grained;darker under PPL and brightly coloured under XPL; main minerals – plagioclase, pyroxene and olivine; often porphyritic (large well-formed crystals in fine groundmass) pyroxene pyroxene

  8. PPL XPLShelly limestoneDark under PPL and dark pearly shades under XPL; main mineral – calcite; note the fossils. calcite calcite

  9. PPL XPLSandstoneRounded quartz fragments; light under PPL and grey/white/black under XPL; main mineral – quartz quartz quartz

  10. PPL XPLArkoseMore angular quartz and feldspar fragments; light under PPL and grey/white/black under XPL; main minerals – quartz and microcline microcline microcline quartz quartz

  11. muddy matrix muddy matrix PPL XPLGreywackeFragments variable in shape, size and type; light under PPL and grey/white/black under XPL; main mineral – quartz but with rock fragments, feldspar and minor micas; look out for the muddy matrix! quartz quartz rock fragment rock fragment

  12. PPL XPLMarbleCrystalline with perfect cleavages evident;light under PPL and pearly shades under XPL; main mineral – calcite. calcite calcite

  13. PPL XPLSchistMinerals showing foliation; light under PPL and brightly coloured under XPL; mainminerals – muscovite, biotite, garnet, quartz and feldspar muscovite muscovite garnet garnet quartz quartz

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