mineralsundermicro_tcm4-285385
DESCRIPTION
mineral (optical minerals)TRANSCRIPT
The MINERALS you need to know
• quartz• microcline• plagioclase• muscovite• biotite• amphibole• pyroxene• olivine• garnet• calcite
Microclinegrain in centre showing its distinctive cross-
hatched twinning
XPLPPL
microcline microcline
Muscovite clear under PPL but with perfect cleavage and
bright interference colours
XPLPPL
muscovite
muscovite
PPL XPL
Biotitepleochroic with one perfect cleavage; strong
natural colour masks polarisation colours making look greenish under XPL
XPL
PPL : lower view rotated to show pleochroism
biotite
biotite
biotite
feldspar
feldspar
Amphibolepleochroic with 2 cleavages at 60o or 120o distinguishing it from biotite or pyroxene
XPL
PPL : lower view showing pleochroism
amphibole
amphibole
Pyroxenewell-formed crystal seen here with 2 cleavages at 90o:
brightly coloured under XPL
XPLPPL
pyroxenepyroxene enlarged
Olivinelooks like a stained-glass window; bright interference
colours and thick black fractures
PPL XPL
olivineolivine
plagioclase plagioclase