red colour of ruby crystal is due to
Ruby A ruby is a pink to blood-red colored gemstone, a variety of the mineral corundum (aluminium oxide). Other varieties of gem-quality corundum are called sapphires. Ruby is one of the traditional cardinal gems, together with amethyst, sapphire, emerald, and diamond.[3] The word ruby comes from ruber, Latin for red. The color of a ruby is due to the element chromium.