Green sapphire and diamond ring, circa 1900. Sapphires come in a vast array of natural colours, depending on the impurities in their crystal structure. The cushion-shaped sapphire at the centre of this ring owes its subtle shade of sage green to iron impurities. Green sapphires are increasingly appreciated for their unique colour palette, which is markedly different from other green stones such as emerald and peridot, but their rarity and relative obscurity means that their prices have not yet caught up with the more famous blue, yellow or pink varieties of sapphire. Set in an elegant Edwardian ring with slender diamond-set shoulders, this is a particularly beautiful choice for an antique engagement ring.