Citrine is the clear yellow or golden form of the mineral quartz. Therefore it is related to amethyst, the purple form of quartz, and to rock crystal, the colourless variety. In fact, a large amount of the citrine used in the jewellery industry is in fact amethyst which has been heated to permanently turn its colour to gold. The colour of citrine is due to small amounts of iron impurities in the crystal structure of quartz, and the difference between citrine and amethyst is only the oxidation state of the iron impurities present in the quartz.
The name is derived from the colour - the yellow of the lemon. The most sought-after stones, however, have a clear, radiant yellow colour. Citrine is frequently confused with topaz, particularly as it is sometimes called topaz quartz to identify its colour. However, the two gems are in fact separate minerals and should not be confused.
Although natural citrine is rare, it can be found in some areas, including Brazil, which is the leading producer of mined citrine. Most of its production comes from the state of Rio Grande do Sul.
In the past, citrine was carried as a protection against snake venom and evil thoughts.