ESCI204 - THIN SECTION REVISION

olivine PPL
- high relief
- typically colourless
- no cleavage

olivine XPL
- max. interference colours
-orthorhombic
-straight or symmetrical extinction

Orthopyroxene PPL
- moderately high relief
- stubby crystals
- typically colourless
- can be pleochroic

Orthopyroxene XPL
- max interference colours
- simple twinning
orthorhombic

clinopyroxene PPL
- moderately high relief
- stubby crystals
- typically colourless but in metamorphic ,, green
-2 cleavage at 90 degrees

clinopyroxene XPL
- max interference colours
- simple twinning
- monoclinic
- inclined extinction of one twin at 45 degrees

Amphibole PPL
- moderate relief
- army green pleochroic ,, brown, blue-green, tan and purple
cleavage 60/120 degreed
- usually elongated crystals

Amphibole XPL
- max. interference colours
- untwinned or lamellar twinning
-monoclinic, long cuts
- small angle extinction - 20/30 degrees

Biotite PPL
- moderate releif
-one perfect cleavage
-strong pleochroism, darkest e-w

Biotite XPL
- bright second order interference colours
- parallel extinction

muscovite PPL
- moderate relief
-one perfect cleavage
- colourless

muscovite XPL
- max. interference colours
-parallel extinction

chlorite PPL
- moderate relief
- one perfect cleavage
- colourless/light green
-pleochroic

chlorite XPL
- low interference colours ,, grey, ink blue, tobacco brown
- parallel extinction

Garnet PPL
- high relief
- no cleavage
- transparent/colourless

Garnet XPL
- isometric, so isotropic (black)
- can have inclusions

staurolite PPL
- high relief
- spongy porphyroblasts
-faintly pleochroic in honey-yellow

Staurolite XPL
- low order colours, brown or yellow

Andalusite PPL
- med-high relief
-colourless
- if blocky cleavage traces paralell sides of block

Andalusite XPL
- first order interference colours

Sillimanite PPL
- med/high relief
- colourless
-fibrolite,, looks like chopped hair
-elongate ,, look for square sections with diagonal cleavage

Sillimanite XPL
- 2nd order interference colours / 1st

Kyanite PPL
- high relief
- colourless
- 2 cleavages ,, one stronger at around 90 degress

Kyanite XPL
-first order interference colours

quartz PPL
- low relief
- no cleavage
- colourless
- often looks like bubbles/ round blobs

quarts XPL
- low first order interference colours (grey, white, maybe dull yellow)
- may show undulatory extinction

Plagioclase PPl
- low relief
- 2 cleavages at 90 degrees
- commonly dusty looking

Plagioclase XPL
- low first order interference colours
- multiple lamellar twinning
- extinction zooms in and out

k-feldspar PPL
- low relief
- 2 cleavages at 90 degrees
- commonly dusty looking

K-feldspar XPL
- first order (grey-white)
- extinction zooms in and out
orthoclase: big single twins
microcline: cross hatch twinning

calcite PPL
- differing relief
- rhombohedral cleavage
- lamellae may be visible in rainbow bands

calcite XPL
- extreme high order white interference colours
- speckled extinction
-deformation lamalle

Tourmaline PPL
- moderate relief
- yellow in colour
- intense pleochroism

Tourmaline XPL
-pleochroism
- lack of cleavage