Sapphire
The name “sapphire” belongs to the mineral species corundum that’s not red and doesn’t qualify as ruby. Besides blue sapphire and ruby, the corundum family also includes so-called “fancy sapphires”. They come in violet, green, yellow, orange, pink, purple and intermediate hues. The mineral corundum is composed only of aluminium and oxygen, and it requires a growth environment that’s free of silicon. In its purest state, corundum is actually colourless. Colourless sapphires were once popular diamond imitations. Sapphires have a hardness of 9 on the MOH's scale of hardness.
