Opal

Grey years ago a man lived in the East, Who did possess a ring of worth immense From a beloved hand. Opal the stone, which flashed a hundred bright and beauteous hues, and had the power to make beloved of God, and Man the blessed and fortunate. — Lessing, in his book Nathan The Wise

The beautiful play of colours across the opal is produced by the way in which light is affected by the gem’s three dimensional lattice, which in turn is made up of tiny spheres of amorphous silica, rather than a regular patron of crystals.