The alpha-alumina or corundum is the most stable chemical compound, and it boasts a hardness of 9 on the Moh’s scale. It is a crystalline type of aluminum oxide (A1 20 3) typically containing aluminum, titanium, vanadium, and chromium traces.
It is a rock-forming mineral, and it is also a naturally transparent material but can possess different colors depending on transition metal impurities in its crystalline structure. Corundum has two significant kinds of gems, including rubies and sapphires. Rubies are red because they contain chromium.
Sapphires display a wide array of colors depending upon which transition metal is present. Corundum can be found in igneous, metamorphic, and sedimentary rocks, and when the type of hardness demonstrated within crystals creates the right material for cutting gemstones.