Citrine

Citrine is the yellow to golden variety of quartz, the crystalline form of silicon dioxide (SiO₂), colored by trace amounts of iron. Natural citrine is one of the rarest members of the quartz family. It forms when trace amounts of iron (Fe³⁺) are incorporated into the quartz crystal structure during growth, and the specific oxidation state of those iron atoms produces a yellow to golden color rather than the purple of amethyst.

The geological conditions required are narrow - the iron must be in the right oxidation state, the growth temperature must be within a specific range, and the crystal must avoid the natural irradiation that would push it toward smoky quartz. This is why genuine citrine is far less common than amethyst, even though both are colored by iron.

The vast majority of citrine sold commercially is actually heat-treated amethyst. When amethyst is heated to 470-560 degrees Celsius, the iron impurities change oxidation state, shifting the color from purple to yellow-orange. This treatment is permanent and stable, but the resulting color tends toward a deeper, more orange-burnt tone that differs from natural citrine's typically softer, champagne-like hue.

Natural citrine ranges from pale champagne yellow to a warm golden honey color. It often shows subtle color zoning and may have a slight smoky quality. The key diagnostic challenge is distinguishing natural citrine from heat-treated amethyst.

Heat-treated stones tend to show a more saturated orange-brown color, often with a reddish tint, and may display white opaque streaks (remnants of the amethyst's original inclusions that didn't survive the heating process). Natural citrine almost never reaches the deep burnt-orange color that heated material achieves. At Mohs 7, citrine is hard and durable. It has no cleavage and fractures conchoidally, just like all quartz varieties.