Citrine

Citrine is quartz coloured yellow to orange-brown by iron. Natural citrine is genuinely uncommon — far rarer than amethyst, which is the same mineral with the same iron in a different oxidation state.

That relationship is the whole commercial story. Heating amethyst to somewhere between 400 and 550 °C converts it to yellow or orange, permanently, and the great majority of citrine on sale has arrived that way. It is not a fake: it is quartz coloured by iron, which is what citrine is. It is a treatment, it is standard, and it is disclosed at the trade level and very often not at the counter.

Much of what is sold as citrine in the deeper reddish-orange shades is heated Brazilian amethyst, and the colour is a reliable indicator: natural citrine tends to a paler, more lemon yellow.

Quartz's hardness of 7, its lack of cleavage and its conchoidal fracture identify the species; the colour identifies the variety. Distinguished from yellow topaz by hardness and from citrine-coloured glass by the absence of bubbles and by its birefringence.

Heated amethyst often shows colour concentrated near the crystal tip and a slight reddish cast, where natural citrine is more evenly and palely coloured.

Gemstone, and one of the more affordable ones because quartz is abundant and large clean pieces are ordinary. Faceted, carved and used in beads.

One of the traditional November birthstones, alongside topaz.

From the French citron, lemon, by way of a Latin root — a straightforward colour name, and one that has been applied historically to yellow stones that were not quartz at all, including topaz.