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ROCKS under the microscope

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Presentation on theme: "ROCKS under the microscope"— Presentation transcript:

1 ROCKS under the microscope

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

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

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

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

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

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

8 calcite calcite PPL XPL Shelly limestone Dark under PPL and dark pearly shades under XPL; main mineral – calcite; note the fossils.

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

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

11 muddy matrix muddy matrix quartz quartz rock fragment rock fragment PPL XPL Greywacke Fragments 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!

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

13 muscovite muscovite garnet garnet quartz quartz PPL XPL Schist Minerals showing foliation; light under PPL and brightly coloured under XPL; main minerals – muscovite, biotite, garnet, quartz and feldspar


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