The ruby is one of the four 'great' precious stones (alongside the diamond, sapphire and emerald), a variety of the mineral corundum of a deep red colour given by a trace of chromium. The ruby is exceptionally hard (second only to diamond), and the most valuable stones have a saturated 'pigeon's blood' hue. For centuries the ruby symbolised passion, strength, power and protection, worn by monarchs and warriors as a talisman stone. In jewellery the ruby is prized for its fiery brilliance and rarity — large clean rubies cost more than diamonds of the same size. It is set in rings, necklaces and earrings when a deep, dramatic accent of colour is wanted.
