Mafic pegmatites cut serpentinite in Precambrian gneisses. Three varieties contain (a) vermiculite only; (b) vermiculite and corundum; or (c) calcic plagioclase, vermiculite, and corundum (plumasitic type). Chemical compositions suggest a trend from anorthosite through plumasite to vermiculite-corundum pegmatite. The absence of primary olivine suggests emplacement temperatures below 500 degrees C. Gems are rubies and sapphires.

First Page Preview

First page PDF preview
You do not currently have access to this article.