General · 1 September 2026
Sapphire and ruby are chemically the same mineral, corundum, but different colours
September's birthstone, sapphire, and July's ruby are actually the same mineral, corundum, which is a crystalline form of aluminium oxide. The dramatic colour differences come from tiny amounts of chemical impurities replacing some aluminium atoms in the crystal. For example, blue sapphire gets its colour from iron and titanium, while chromium makes corundum red, which gemologists then call ruby.
Reported by American Council on Science and Health · How we write briefs