Zircon has been known since antiquity and the faceted stones display great brilliance and an intense fire. Zircon is most famous for its colourless stones, which closely resemble diamonds and have been used both intentionally and mistakenly in their place. Zircon can be distinguished from diamond because it is a softer stone and its facets will show wear and tear. Although zircon is colourless when it is pure, impurities in its composition will produce yellow, orange, blue, red, green and brown varieties. Brown varieties are usually heat treated to make the more popular colourless and blue stones for use in jewellery.