A naturally occurring silicate of zirconium, ZrSiO₄, used as a gemstone. The colour depends in small amounts of other metals and may be red, brown, yellow, or green. Red gem-quality zircon is sometimes called jacinth; gem-quality zircons with other colours are called jargoons. There is also a naturally occurring colourless variety. Zircon gems can be given other colours, or made colourless, by heat treatment. The colourless varieties (either natural or treated) are sometimes called Matura diamonds (after Matura in Sri Lanka). The name ‘zircon’ is often erroneously applied to a synthetic form of the oxide cubic zircona, which is used as a diamond substitute.