Some opaque sapphires, when cut en cabochon, display a fascinating white six-rayed star which changes position as the stone is turned. These gems are known by the scientific name of asteria or more commonly called, star sapphires. During the formation of these stones, small needle-like inclusions of rutile occur in hexagonal patterns causing multiple internal reflections when light shines upon the polished surface. A booklet published by Marcus & Co. in 1938 entitled, The Story of the Sapphire and the Ruby noted that 'Nature has endowed only a small proportion of corundum (the mineral of which sapphire and ruby are varieties) with this elusive property'.