The corundum family of gemstones consists of ruby and sapphire. Corundum is very compact, dense, and lacks gemstone cleavage. It’s also the second hardest natural mineral after diamond. Gem-quality corundum is also quite rare. These factors make both varieties of corundum some of the most highly desired jewelry stones. Ruby is the red variety of corundum. All other colors of corundum, including colorless, are called sapphires.
Rubies and sapphires are some of the most valuable and popular of all gemstones. Despite the enormous size of these stones in museums and royal collections, most corundum gems available for sale are usually of more modest size. A 3-4 carat ruby of fine quality would be a rare and very expensive gem in today’s market. Sapphires over 5 carats, clean and with good blue color, are similarly rare and also valuable. Relatively speaking, there is an abundance of good quality small sapphires but not rubies. Very few known ruby deposits can be actively worked, while there are many more sapphire deposits being actively mined.
Sapphires, in general, reach a far greater size than rubies. A ruby of 30 carats is a great rarity, whereas sapphires in museum collections weighing hundreds of carats are not uncommon. The largest rubies come from the chrome-zoisite matrix in Tanzania, but these are not really of gem quality. Fine gem rubies of large size occur in the Sri Lankan gravels, with smaller ones from Burma and Thailand. Enormous sapphires of fine color and transparency have been found in the gem gravels of Sri Lanka and Burma. (Most are from Sri Lanka). A 1400 gram ruby was found in Yugoslavia (Prilip) but was not gemmy. Malawi material (sapphire) reaches a size of about 12 carats. Large sapphires have been found in Australia. Montana sapphires over 1 carat are very rare, but the blue ones in this size range are magnificent.
Corundum is found in metamorphosed rocks such as gneiss and schist. Gneiss and Schist formations in B.C. are known to exist at Kinbasket Lake, Kootenay Lake , Vernon, and Prince Rupert areas. Gem quality sapphire pebbles of light green colour have been found in the Pend Oreille River. Rubies of minute grains have been found in some of the tributary creeks of the Tulameen River.