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Muscovite Mica

 

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Muscovite Mica  (Click PPL image to show labels)

Olivine

 

Muscovite in a garnet schist. Masses of elongated muscovite laths, more or less parallel.

Generally colourless with one cleveage direction. Dark colour a result of impurities inherited from the original sedimentary rock.

 

Width of field of view: 8mm.

 

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Olivine XPL view

 

Muscovite in schist. Bright interference colours. Parallel extinction and high degree of alignment give a general colour on/off effect as the slide is rotated. At or near extinction muscovite shows a quite characteristic "speckled" appearance, common to most micas.

 

Width of field of view: 8mm.

 

 

   

 

   

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Olivine rollover

 

Muscovite in a staurolite garnet schist. Larger individual laths than above.

 

Width of field of view: 12mm.

 

 

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Muscovite in schist. Musvovite seems to 'flow' round other porphryoblasts, but this is not caused by any sort of flow, re-crystallisation having taken place while the rock is solid.

 

Length of central (blue) crystal: 2.5mm

 

 

 

   

 

   

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Olivine rollover

 

Muscovite in a granite pegmatite. While muscovite is most often found in metamorphic rocks, is does occur, usually in very minor quantities, in igneous (usually acid) rocks. This is a quartz/muscovite intergrowth in a mainly orthoclase pegmatite.

Other types of pale mica, with many different varietal names, are found in altered granites, greisens, ores, and contact metamorphics. They are optically very similar, and chemical analysis may be required for exact identification.

 

Width of field of view: 8mm.

 

 

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Muscovite in granite pegmatite. Intergrowth texture, no schistose texture as seen in metamorphic rocks.

 

Width of field of view: 8mm.

 

 

 

   

 

   

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