For use in jewellery, most opal is cut and polished to form a cabochon, a convex shape that maximises the viewing angles through which an opal's play of colour can be observed. "Natural" opal refers to polished stones consisting wholly of precious opal.
Photos of opal from around the world. Guidance for people who want to buy opal, see different types of opal, understand their names, learn about synthetics and imitations.
Opal, silica mineral extensively used as a gemstone, a submicrocrystalline variety of cristobalite. In ancient times opal was included among the noble gems and was ranked second only to emerald by the Romans.