22/5/13 Garnet

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Garnet

Mineral structure: Single SiO4 structure silicate (orthosilicate)

Common mineral in Pelites and Metabasic rocks (Medium to High grade),

Rock-forming minerals associated with Garnet: Muscovite, Biotite, Amphibole, Pyroxene

Garnet in Schist

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Key optical features of garnet in thin section:

Colourless to Brown

No cleavage High relief Isotropic

Commonly forms equant porphyroblasts (inclusions are common)

Common minerals that might be confused with garnet and occur in similar rocks: Few other minerals of high relief are isotropic, Spinel tends to be both smaller and more strongly

coloured.

Alteration of garnet to chlorite

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22/5/13 Garnet

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Garnet porphyroblast in muscovite – biotite schist

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Note: Quartz inclusions are commonly present sometimes as different trails within large garnetporphyroblasts

Garnet porphyroblasts in metabasic amphibolite

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Note: Abundant green amphibole with isotopic high relief garnet

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