Carbonate Minerals

Steven Dutch, Natural and Applied Sciences, University of Wisconsin - Green Bay
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Plane-Polarized Light

• Calcite, Dolomite, Siderite and other common carbonates are almost indistinguishable in thin section.
• Extremely high relief
• Colorless, but tends to be grainy in appearance. The extremely high relief means even the tiniest irregularities stand out.
• Perfect rhombohedral cleavage

Crossed Polarizers

• Extremely high order interference colors. Has a pearly appearance because of tiny patches of color. Even the slightest variation in thickness due to grinding results in noticeable color variation.
• Twin bands are common (A). These often have moderate but highly mottled color because the crystallographic orientation in the twin band partially cancels out the interference color of the rest of the crystal. Calcite is extremely ductile and these are often due to deformation.

Calcite in plane polarized light.

In crossed polarizers, the interference colors are extremely high order and twin lamellae are common.

The specimen below, seen in crossed polarizers, shows iridescent twin lamellae.

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Created 22 Sept 1997, Last Update 14 Sep 2009

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