Garnet

Garnet
Property	Value	Comments
Formula	Pyrope: Mg₃Al₂(SiO₄)₃Almandine: Fe₃Al₂(SiO₄)₃Spessartine: Mn₃Al₂(SiO₄)₃Grossular: Ca₃Al₂(SiO₄)₃ Andradite: Ca₃Fe₂(SiO₄)₃Uvarovite: Ca₃Cr₂(SiO₄)₃	Compositions can be expressed by the general formula A₃B₂(SiO₄)
Crystal System	isometric
Crystal Habit	rounded grains, massive granular (coarse or fine)
Cleavage	no distinct cleavage	irregular conchoidal fracture
Color/Pleochroism	Pyrope: deep red to nearly black Almandine: deep red to brownish red Spessartine: brownish to red Grossular: white, green, yellow, brown, pale red Andradite: yellow, green, brown, black Uvarovite: emerald-green
Refractive Index	1.714-1.890
Distinguishing Features	High relief in thin section. Color in thin section is a pale version of the hand sample color. H=7.5. White streak.
Occurrence	Pyrope: ultramafic igneous rocks Almandine: typical garnet in mica schist and gneiss Spessartine: felsic igneous rocks Grossular and andradite: typical garnets found in metamorphosed carbonate-rich rocks.
Editors	Sarah Vorhies (06)

	Photomicrograph of a mostly almandine garnet in plane polarized light. Click on the thumbnail to see a larger ppl/xpl rollover image.
	Photomicrograph of garnet in cross polarized light.