Sapphire
SAPPHIRE, a precious stone with a blue color (Exod 24:10). Like ruby (q.v.) it is a variety of corundum (aluminum oxide) which, next to diamond, is the hardest known naturally occurring mineral. The blue color of sapphire is thought to be due to titanium. However, the blue colored mineral lapis lazuli (q.v.) may have been referred to as sapphire by some early writers (cf. KJV and NEB Exod 28:18). Sapphire possesses a fibrous structure which is generally very faint. Where this structure is well developed, an optical effect of six rays of light emanating from a center is shown and the precious stone is called a star sapphire. The term sapphire has also been used to refer to all gem varieties of corundum except those that are red (rubies); these include oriental topaz (yellow), oriental emerald (green) and oriental amethyst (purple). The transparent colorless variety is called white sapphire; it has been referred to by some writers as adamant (q.v.). Sapphire, together with ruby and many other gem stones have come from Ceylon for 2,500 years. They mainly occur in detrital gravels derived from the denudation of metamorphic rocks, including crystalline limestones. They are also obtained from the basement crystalline rocks.
Bibliography
E. S. Dana, A Text-book of Mineralogy, 4th ed. (revised by W. E. Ford) (1932), 481-483; A. M. Bateman, Economic Mineral Deposits, 2nd ed. (1950), 847, 848.