Steven Dutch, Professor Emeritus, Natural and Applied Sciences, Universityof Wisconsin - Green Bay

Plane-Polarized Light

Crossed Polarizers

In plane-polarized light, garnet is clear and has very high relief. The light brownmaterial is biotite. Most of the clear material is quartz.

GARNETP1.jpg (61580 bytes)

In crossed polarizers, garnet is isotropic. The black areas are larger than the visiblegarnet above because of plucking - part of the garnet broke off the slide during thegrinding process.

GARNETX1.jpg (71212 bytes)

Garnet often is euhedral, as in the plane-polarized view below. This garnet is lightpinkish. The light green material around it is an amphibole called omphacite. The rock isan eclogite, a metamorphic rock from the upper mantle.

GARNETP2.jpg (75950 bytes)

In crossed polarizers the euhedral form of the garnet stands out sharply. Note thenumerous inclusions.

GARNETX2.jpg (97949 bytes)

Below, a fairly typical small garnet seen in plane-polarized light.

garnetp3.jpg (215264 bytes)

The same field is seen below in crossed polarizers.

GARNETX3.jpg (97308 bytes)

Below, at left, is a very large garnet filling the entire field and enclosing numerousquartz inclusions. At right is the same field under crossed polarizers.

GARNETP4.jpg (87028 bytes) GARNETX4.jpg (82295 bytes)

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Created 22 Sept 1997, Last Update 17 December, 1997