Sapphire, a not so simple gemstone

Abstract

Sapphire is a gemstone of considerable reach and much studied, and yet still delivering scientific surprises. This is most recently exemplified by a new paper in this issue of American Mineralogist by Palke and Breeding (2017) that re-interprets the origin of needle-like rutile inclusions that form “silk” in sapphires. Sapphire as a gem variety of corundum with wide use in the gem trade as one of the more historically valuable colored gem stones (CGS). It is mined from a great variety of continental gem deposits across the world. A masterly compendium on this gemstone and its ramifications is available (Hughes 2017). As a gem, sapphire ranges through all the colors of corundum, except where sufficient Cr enters its α-alumina crystal structure and causes the red color characteristic of the variety ruby. Sapphire, as a key pillar in a wide economic network of gem-enhancing treatments, jewelry, and other manufacturing enterprises, has elicited numerous scientific and gemological enquiries into its internal nature and natural genesis and subsequent treatments. A further use of sapphire as a synthetic material with a great variety of purposes also has triggered a proliferation of detailed studies on its growth, properties, and other element substitutional effects (Dobrovinskaya et …