Petrographic Thin Sections Used to examine microscopic structure of rocks.

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Presentation transcript:

Petrographic Thin Sections Used to examine microscopic structure of rocks

Polarizing Microscope Use "polarizing" or "petrographic" microscope.

Thin Sections small slabs of rock sample glued to a glass slide ground to a specified thickness of 0.03mm (30 microns)

Types of Light Plane Light –single plane. –sine wave vibration in polarization plane. Cross Polarized Light –two planes –2 sine wave vibrations perpendicular (crossed)

Rock Textures Phaneritic –separate grains appear Pheocrystic/Porphyritic –large grains in “groundmass” Aphanitic –grains not visible to eye

Mineral Light Properties Isotropic minerals –show same velocity of light in all directions –same colors Anisotropic minerals –show the velocity of light varying in different orientations –different colors

Mineral Appearances MineralPlane LightCross Light Quartzclearshades gray Biotitebrownbright pastels Muscoviteclearblue speckle

Mineral Appearances MineralPlane LightCross Light K-feldsparplaid plagioclas feldspar pinstripe horneblend e brown 120° cleavage bright

Mineral Appearances MineralPlane LightCross Light Garnethigh tan black Calcite rhomboid cleavage