Ruby is a pink to blood-red coloured 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. ... The world's most valuable ruby is the Sunrise Ruby. Shop any of our ruby loose gems now and even customize any 18K Engagement Ring/Pendants/Earrings etc.