Sapphire jewelry. They also may be created synthetically in laboratories for industrial or decorative purposes in large crystal boules. Because of the remarkable hardness of sapphires – 9 on the Mohs scale (the third hardest mineral, after diamond at 10 and moissanite at 9.5) – sapphires are also used in some non-ornamental applications, such as infrared optical components, high-durability windows, wristwatch crystals and movement bearings, and very thin electronic wafers, which are used as the insulating substrates of very special-purpose solid-state electronics (especially integrated circuits and GaN-based LEDs). Sapphire is the birthstone for September and the gem of the 45th anniversary.
Birthstone of the Second Temple, not the one described in Exodus. St. Jerome, referencing Josephus, said the Foundation Stones of the New Jerusalem (Revelation 21:19–20) would be appropriate for Christians to use. In the eighth and ninth century, religious treatises associating a particular stone with an apostle were written, so that "their name would be inscribed on the Foundation Stones, and his virtue." Practice became to keep twelve stones and wear one a month. The custom of wearing a single birthstone is only a few centuries old, though modern authorities differ on dates. Kunz places the custom in eighteenth century Poland,