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

Very common mineral in low-grade metamorphic rocks and as an alteration product of ferromagnesian minerals. Low relief, colorless to green. Light green is most common shade. Micaceous cleavage, often matted or feltlike appearance.

Crossed Polarizers

Low birefringence results in first-order whites. Anomalous interference colors very common (A). Dark blue, brown, purple and green are possible. Fine-grained, matted-looking varieties often show undulose extinction.

The light green mass in the center of this plane-polarized view is chlorite. Most of the brownish micaceous mineral around it is biotite.

CHLOR-P1.JPG (65317 bytes)

The crossed-polarizer view below shows dark purple anomalous extinction colors. Chlorite is one of the most common minerals to show anomalous extinction.

CHLOR-X1.JPG (88115 bytes)

Another common appearance of chlorite. In this crossed-polarizer view we see parallel blades of chlorite, very similar in texture to mica, but distinguished by first-order white interference colors. Again, we also see dark purple anomalous extinction.

CHLOR-X2.JPG (69729 bytes)

The plane-polarizer view below shows a field mostly of light green chlorite, with two opaque magnetite crystals at the top.

CHLOR-P3.JPG (51867 bytes)

The same field in crossed polarizers. The chlorite is actually a mass of criss-crossing small plates, giving the material a felt-like texture. This is a very common texture in chlorite. Note that these extinction colors are normal. Not all chlorite shows anomalous extinction.

CHLOR-X3.JPG (97289 bytes)

The plane-polarizer view below is pretty typical of greenschist facies metamorphic rocks. The brown is biotite, the light green is mostly chlorite, and the darker green includes hornblende (note one grain with 56-124 cleavage just below left center).

CHLOR-P4.JPG (79228 bytes)

In the crossed-polarizer view below, the chlorite stands out because of its anomalous extinction colors.

CHLOR-X4.JPG (95232 bytes)

In the impure quartzite below, the clay filling between the quartz grains has been metamorphosed to bright green chlorite.

CHLOR-P5.JPG (51523 bytes)

The same field in crossed polarizers. The chlorite is a fine-grained felt-like mass showing first-ordred whites and normal extinction colors.

CHLOR-X5.JPG (55764 bytes)

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Created 10 Oct 1997, Last Update 14 Dec 2009

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