EOSC 118 Lecture Notes - Lecture 18: Baffin Island, Soyou, Current Science
Document Summary
The geology of gem corundum three main genetic models: Sapphires and rubies are classified by locality or country. This is a reasonable approach except to geoscientists and those who recognize that the rocks that host these stones will always transcend geographical names and political boundaries. Many different gem-producing localities and countries can have almost identical geological settings. Conversely, a single gem-producing area can have several geological settings that give rise to similar stones. Corundum (al2o3) actually occurs in many rock types and is not uncommon and is found the world over. The primary factor for its presence is low abundance of silica (sio2). When both silica and aluminum are present in a growing environment, they will be incorporated into aluminosilicates (minerals containing. Al and si), inhibiting the growth of corundum. In addition to low si, an environment with trace amounts of fe, cr, and ti will promote the formation of gem corundum.
