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Garnet

 

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Garnet  Pyrope / Almandine ~ see index for others.(Click PPL image to show labels)

Olivine

 

Garnet in a mica schist. Variously shaped porphyoblasts usually red/brown in hand sample but often not strongly enough coloured to show colour in thin section. Randomly orientated cracks are very common. Isotropic, so no pleochroism.

 

Width of central crystal: 2mm.

 

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Olivine XPL view

 

Garnet in schist. Isotropic, so always black in XPL (except in very rare circumstances)

 

Width of central crystal: 2mm.

 

 

   

 

   

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Olivine rollover

 

Garnet in a mica schist. Shows internal zoning and spiral inclusions indicating rotation whilst growing. Lines of inclusions within the porphyoblast are relicts from the layered structure of the original sedimentary rock.

 

Average width of crystals: 2.5mm

 

 

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Garnet in schist. White spots in the garnets are quartz inclusions.

 

Average width of crystals: 2.5mm

 

 

 

   

 

   

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Olivine rollover

 

Garnet in a granite pegmatite. Garnets are uncommon in igneous rocks (except alkali syenites) but sometimes occur as in this pegmatite, aling with tourmaline and ?beryl. subhedral grains, again showing cracking.

 

Width of field of view: 8mm

 

 

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Garnet in a pegmatite. Isotropic and black in XPL.

 

Width of field of view: 8mm

 

 

 

   

 

   

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Olivine rollover

 

Garnet in an eclogite, a rare ultrahigh pressure metamorphic rock, often derived from a basalt or similar. Granular texture, rounded shapes. No pleochroism in PPL.

 

Width of field of view: 6mm

 

 

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Garnet in eclogite. Black as always in XPL.

 

Width of field of view: 6mm

 

 

 

   

 

   

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