rocks under the microscope. the rocks you need to know granite diorite gabbro dolerite basalt shelly...
Post on 28-Mar-2015
230 Views
Preview:
TRANSCRIPT
ROCKS
under the microscope
The ROCKS you need to know
• granite• diorite• gabbro• dolerite• basalt• shelly limestone• sandstone• arkose• greywacke• marble• schist
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
quartzquartz
muscovite
muscovite
biotitebiotite
plagioclaseplagioclase
plagioclase
amphibole
amphibole
plagioclase
biotite biotite
PPL XPL
Diorite
Darker under PPL than granite with more coloured minerals; much plagioclase and amphibole/biotite, only small amount of quartz
PPL XPL
Gabbro Coarse-grained; darker under PPL and brightly coloured under XPL; main minerals –
plagioclase, pyroxene and olivine
olivine
olivine
olivine
pyroxenepyroxene
plagioclaseplagioclase
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
plagioclase plagioclase
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)
pyroxenepyroxene
fine groundmass of
plagioclase & iron minerals
calcite calcite
PPL XPL
Shelly limestone Dark under PPL and dark pearly shades under XPL; main mineral – calcite; note the
fossils.
quartzquartz
PPL XPL
Sandstone Rounded quartz fragments; light under PPL and grey/white/black under XPL; main
mineral – quartz
microcline
quartz quartz
microcline
PPL XPL
Arkose More angular quartz and feldspar fragments; light under PPL and grey/white/black under
XPL; main minerals – quartz and microcline
quartzquartz
muddy
matrixmuddy
matrix
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!
calcitecalcite
PPL XPL
Marble Crystalline with perfect cleavages evident; light under PPL and pearly shades under XPL;
main mineral – calcite.
garnet
muscovite
quartz
PPL XPL
Schist Minerals showing foliation; light under PPL and brightly coloured under XPL; main
minerals – muscovite, biotite, garnet, quartz and feldspar
garnet
muscovite
quartz
top related