Citrine is a variety of quartz, which means it shares the same silicon dioxide composition. But unlike clear rock crystal quartz, citrine's color results from trace amounts of iron within the crystal structure. The iron acts as an impurity, causing the quartz to range in hue from pale yellow to amber brown. The name citrine comes from the French word "citron," meaning lemon.
True natural citrine is formed when iron in a quartz crystal oxidizes, creating the yellow to orange coloration. This oxidation process can occur naturally when quartz is exposed to air over extremely long periods of time. Natural citrine has also been found near iron ore deposits where iron leaches into the quartz.
Most citrine on the market today is not naturally occurring, however. The majority of citrine is heat treated amethyst iron-free quartz that turns yellow when exposed to high temperatures of 470 to 550 degrees Celsius. The heat-treated material has the same chemical composition as natural citrine, and it displays the same colors.
Why Natural Citrine is Uncommon
For natural citrine to form, very specific conditions are required. First, the quartz must contain trace amounts of iron. Next, the iron needs to oxidize to create the citrine coloration. This oxidation process happens slowly over thousands of years when quartz is exposed to oxygen. Oxidation can also take place more quickly when quartz forms near iron ore deposits. But opportunities for this type of citrine formation are extremely limited.
Additionally, natural citrine often forms together with amethyst – the purple quartz variety. Many geodes are found with amethyst on the outside and citrine quartz on the inside. Here, the iron was able to oxidize in the inner regions of the geode where oxygen was present, while the outer amethyst layer was protected from this color change. Much of the world's citrine is mined in geode deposits, where natural citrine formation is dependent on this very specific set of circumstances.
There are only a few mines in the world that produce true natural citrine crystals on a large commercial scale. The largest sources are in Rio Grande do Sul, Brazil where iron-richquartz geodes can be found. This region produces natural citrine ranging from pale yellow to deep orange-brown. Other sources for natural citrine include the Ural Mountains in Russia, Madagascar, and the United States. But from these locations, natural citrine occurs only rarely.
By contrast, iron-free amethyst is abundantly present in geodes, clusters, and crystal formations. Some of the largest supplies come from Brazil, Uruguay, and Zambia. When this plentiful amethyst is heat treated, it readily transforms into the yellow and orange hues of citrine.
How Natural and Treated Citrine Differ
To the naked eye, natural and heat-treated citrine can look identical in color and clarity. They share the same chemical composition and hardness as well. Both have a vitreous luster and display the lovely yellow to orange hues so desired in citrine gemstones.
But heat-treated citrine tends to have a uniform color throughout a single stone. Natural citrine more often displays zoning with color variations within a single crystal. Under a microscope, natural citrine will show irregular fluid inclusions, tiny interior flaws that indicate the gem's natural growth process. Heating usually eliminates most inclusions, leaving heat-treated citrine clean inside.
Advanced gemological testing can also differentiate natural vs. treated citrine. Infrared spectroscopy reveals differences in the trace iron absorption spectra. And extended exposure to heat will cause heat-treated citrine's yellow color to fade back to purple, while natural citrine is stable. But for the average consumer, it's nearly impossible to distinguish treated from natural citrine.
Should You Only Buy Natural Citrine?
Given the scarcity of natural citrine, most gemstones on the market, even those labeled "natural," are heat-treated amethyst. As a buyer, does it matter if you purchase a natural vs. treated stone? Not really, as there are advantages to both.
Natural citrine is incredibly rare, so it comes with higher prices. Top quality natural citrine can cost over $500 per carat. Lower grade natural citrine with flaws may sell for $50 to $100 per carat. By contrast, commercial grade heat-treated citrine sells for as little as $5 per carat.
While natural citrine is rare and unique, heat-treated stones have their own benefits. The treatment allows for pure yellow and orange hues unavailable naturally. Treated citrine also has fewer flaws and is available in large flawless cuts. So you can purchase beautiful jewelry-quality citrine at affordable prices.
For the average consumer, heat-treated citrine provides gorgeous yellow gemstones perfect for jewelry or home decor. Natural citrine is primarily valued by collectors seeking an exceptionally rare gem. But whichever you choose, citrine's sunny beauty has sparked human admiration for centuries – and will continue lighting up jewelry and lives well into the future.
