A ruby gemstone is a variety of the mineral corundum, formed by aluminium oxide with the presence of the element chromium contributing to the red colour. Its name comes from ruber, Latin for red.
With a Mohs rating of 9, rubies are harder than any natural gemstone except a diamond. The most valuable rubies are those with the deepest red – for example “blood-red” rubies command a large premium over other rubies. It is this red colour that has lead people to associate the ruby with love, passion and strength.