Sapphire (which probably referred instead at the time to lapis lazuli) is a gemstone variety of the mineral corundum, an aluminium oxide (α-Al₂O₃). Trace amounts of other elements such as iron,titanium, chromium, copper, or magnesium can give corundum blue, yellow, pink, purple, orange, or a greenish color. Chromium impurities in corundum yield a red tint, and the resultant gemstone is called a ruby.

• Corundum