The most well-known types of corundum are sapphire and ruby.
Corundum can be found in an almost limitless variety of colours: from colourless, red and pink, through blue, black and brown, to orange, yellow, green or purple. The colours are formed by different concentrations of various impurities.
Red corundum and most pink corundum is called ruby, while blue corundum is called sapphire. Other colours are also called sapphire, usually with the colour specified as a prefix to the word sapphire, as in: yellow sapphire.
Corundum can be found globally, but is particularly common in Myanmar (Burma), Thailand and Sri Lanka.