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Minerals under the microscope

Minerals under the microscope. The MINERALS you need to know quartz microcline plagioclase muscovite biotite amphibole pyroxene olivine garnet calcite. quartz. quartz. Quartz grains in sandstone. quartz. quartz. PPL. XPL. plagioclase. Plagioclase with repeated twinning.

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Minerals under the microscope

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  1. Minerals under the microscope

  2. The MINERALS you need to know • quartz • microcline • plagioclase • muscovite • biotite • amphibole • pyroxene • olivine • garnet • calcite

  3. quartz quartz Quartzgrains in sandstone quartz quartz PPL XPL

  4. plagioclase Plagioclasewith repeated twinning plagioclase PPL XPL

  5. microcline microcline Microclinegrain in centre showing its distinctive cross-hatched twinning PPL XPL

  6. Muscovite clear under PPL but with perfect cleavage and bright interference colours muscovite muscovite PPL XPL PPL XPL

  7. feldspar feldspar biotite Biotitepleochroic with one perfect cleavage; strong natural colour masks polarisation colours making look greenish under XPL biotite PPL : lower view rotated to show pleochroism XPL biotite

  8. amphibole amphibole Amphibolepleochroic with 2 cleavages at 60o or 120o distinguishing it from biotite or pyroxene PPL : lower view showing pleochroism XPL

  9. pyroxene pyroxene enlarged Pyroxenewell-formed crystal seen here with 2 cleavages at 90o: brightly coloured under XPL PPL XPL

  10. olivine olivine Olivinelooks like a stained-glass window; bright interference colours and thick black fractures plagioclase plagioclase PPL XPL

  11. Garnetrounded crystal,transparent under PPL but goes extinct under XPL garnet garnet PPL XPL

  12. Calcitemay show both high and low relief, transparent under PPL with 2 perfect cleavages at 120o. Under XPL it shows pearly shades calcite calcite PPL XPL

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