Garnet

Steven Dutch, Natural and Applied Sciences, University of Wisconsin - Green Bay
First-time Visitors: Please visit Site Map and Disclaimer. Use "Back" to return here.

Plane-Polarized Light

• High relief
• Clear, occasionally very light pinkish
• No cleavage
• Euhedral crystals common (A)
• Retrograde metamorphism common (B). Garnet will revert to greenish amphiboles or chlorite, still retaining the original outline of the crystal. Remnants of garnet are often preserved in the interior
• Internal fracturing of grains common
• Crystals commonly contain inclusions, incorporated as the garnet grew.

Crossed Polarizers

• The most common isotropic mineral

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

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

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

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

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

The same field is seen below in crossed polarizers.

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

Return to Thin-Section Index
Return to Mineral Identification Tables
Return to Professor Dutch's Home Page

Created 22 Sept 1997, Last Update 17 December, 1997

Not an official UW Green Bay site