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Calcite

 

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Calcite  (Click PPL image to show labels)

Olivine

 

Calcite in a contact metamorphosed limestone. The calcite has been recrystalised into large irregular grains. Twinning can be seen even in PPL. Cleavage also usually present and can be mistaken for twinning. To see difference use XPL view and rotate.

 

Width of field of view: 9mm.

 

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Olivine XPL view

 

Calcite in metalimestone. Calcite in xpl appears a beige colour which does not vary much with thickness. Birefringence is very high and only shows as pastel tints or not at all.

Highly coloured bands (twinning) is vey common.

 

Width of field of view: 9mm.

 

 

   

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Twinning

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Olivine rollover

 

Calcite in an oolitic limestone. Sedimentary limestones often do not show typical calcite optical characteristics, often as a result of submicroscopic grain size and impurities. Oolites may nucleate on grains or shell fragments.

 

Width of field of view: 9mm.

 

 

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Calcite in oolitic limestone. There is often not much visual difference between XPL and PPL in sedimentary limestones. Grains of other minerals are more visible. More detail is visible if the section is slightly thicker than 30ยต. This may cause grains of quartz to show unexpectedly high birefringence colours.

 

Width of field of view: 9mm.

 

 

 

   

 

   

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Olivine rollover

 

Calcite in a Marble. Recrystalised grains of calcite, none of the original sedimentary structure visible. Bars of colour (twinning) visible even in PPL, a good indicator of calcite.

 

Width of field of view: 7mm.

 

 

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Calcite in marble, beige colour or pale pastel colours. Other minerals prominent with contrasting bright interference colours

 

Width of field of view: 7mm.

 

 

 

   

 

   

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Olivine rollover

 

Calcite in a carbonatite, from a dyke or stock, not a lava. Medium sized blade shaped crystals seem to be common in slowly cooled carbonatites.

 

Width of field of view: 10mm.

 

 

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Calcite in carbonatite. Outlines of the blades are more easily visible in XPL.

 

Width of field of view: 10mm.

 

 

 

   

 

   

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