蓝宝石是刚玉宝石中除红色的红宝石之外，其它颜色刚玉宝石的通称，主要成分是氧化铝（Al₂O₃）为九月的诞生石。

一般认为蓝宝石的英文sapphire源自希腊文sappheiros，意为蓝色的石头。

Sapphire (Greek:σάπφειρος; sappheiros, 'blue stone', itself derived from Sanskrit "ShaniPriya" which probably referred instead at the time to lapis lazuli) is a typically blue gemstone variety of the mineral corundum, an aluminium oxide (α-Al₂O₃). Trace amounts of elements such as iron, titanium, chromium, copper, or magnesium can give corundum respectively blue, yellow, purple, orange, or green color. Chromium impurities in corundum yield pink or red tint, the latter being called ruby.