Citrine is the transparent yellow to orange colored variety of quartz, deriving its name from the Latin, or French “citron” meaning lemon. A better color analogy is with that delightful apertif “sherry”, ranging from fino, Amontillado through to Oloroso.
Citrine is found in inexpensive jewelry and is sometimes mistaken for yellow topaz, with which it shares the honor of being the birthstone for November. I suspect that most, if not all the “topazes” mentioned in the old days were yellow quartz. It wasn’t until modern times that the difference was realized.
Amateur gem cutters often experiment first with citrine rough since it is readily available from Brazil, or your local rock shop. Basically, there are two types of citrine, the large natural pale yellow material, and smaller more deeply colored variety, sometimes of a rich orange hue, which can be made by heat-treating amethyst, and as such it resembles Imperial topaz.
If you get the opportunity to roam around the counrtryside of Goias in Brazil, such as at the village of Cristalina, near Brasilia, do so, for you will find an abundance of quartz gemstones produced by local lapidary families. Small boys come racing after you on bicycle with samples of faceted citrines and smoky quartz contained in cigar boxes hoping to make a sale, for just a few dollars. I purchased a magnificent step-cut citrine, flawless, measuring 45 by 30 mm and lots of smokies and specimen crystals. The children are pretty good at jamb-peg faceting having been taught by their parents.
Smoky quartz is the most common. A gentle heat treatment is often sufficient to drive off the smokiness to give a clear pale yellow. The cause of the yellow color of natural citrine has been attributed to a colloidal dispersion of hydrous ferric oxide, to the extent of ca 0.025% Fe2O3. Amethyst also contains iron at this level of some undetermined type, also sometimes Mn and Ti ions. The color of smoky quartz seems to be due to lattice defects caused by Al substituting for Si (1).
Amethyst can be converted to citrine by heat which is a process known for centuries. Special furnaces are used by the locals to heat amethyst crystals to about 550 degrees C for an hour or so, to produce yellow citrine and the deeper orange colors. The amethyst used may be geode material derived from basalt lavas, and is plentiful in Brazil.
Natural citrine is quite rare in occurrence compared to other varieties of quartz. It is found where amethyst also occurs so one is never sure whether it is the genuine untreated material. However, the prime sources are the Brazilian states of Minas Gerais, Goiaz, and Rio Grande do Sul, also from Uruguay.
Citrine maintains a niche role in inexpensive jewelry. It has a beautiful color and takes a good polish. It is a gemstone to be cherished by all those lucky women who are able to display it to perfection.
“Dana’s System of Mineralogy”, Vol. 3, Silica Minerals, p. 183, John Wiley & Sons (1962).