photo: courtesy of alan guisewite
Grossular garnet comes in two varieties: one is found as transparent crystals (tsavorite), the other is considered "massive" and is used mainly as a decorative stone under the name green garnet
The massive green variety, which may contain up to five per cent water, is called hydro-grossular garnet and can be as large as a boulder, or even as a hill.
Grossular garnet forms by contact metamorphism and can be found in limestone rocks that have reacted with hot molten rock (magmatic inclusions). It may also be found in some igneous rocks.
transvaal area of south africa
Massive green grossular garnet from South Africa is called Transvaal jade
after the area from which it is mined, although it resembles jade only in color.
Given the mineralogical complexity among the many members of the garnet group -- and the resulting melange of colors, green garnet on the market today may actually belong to one of several branches of the garnet family
grossular, demantoid or uvarovite.