Ruby is a red gemstone,a variety of the mineral corundum (aluminium oxide).The color is mainly caused by aluminium.

Rubies are mined in Africa, Asia, Australia,Greenland, andNorth Carolina. They are most often found in Myanmar (Burma), Sri Lanka, Kenya, Madagascar, and Thailand, but they have also been found in the U.S. states of Montana, North Carolina and
South Carolina.

Rubies have a hardness of 9.0 on the Mohs scale of mineral hardness. Among the natural gems only diamond is harder.