Natural citrine is a rare variety of quartz (SiO₂) that gets its yellow to orange-brown color from trace amounts of iron in its crystal structure, naturally heated by geological processes. It has a Mohs hardness of 7, making it durable for jewelry. Major sources include Brazil, Zambia, Madagascar, and Russia.

Heated citrine is amethyst or smoky quartz that has been heat-treated to achieve a yellow, orange, or reddish-brown hue. Most commercial citrine on the market is heat-treated amethyst, typically from Brazil. Heat-treated citrine often has a more intense, reddish-orange color compared to natural citrine, which tends to have a paler, smoky yellow tone.