Contrary to the title of this article, there is no such thing as yellow emeralds. By definition, the color of a beryl mineral qualifying as an emerald is a pure green to bluish green and is not too light. Any colors outside this definition are not emerald.
However, the mineral species of beryl can be vividly yellow. This variety is referred to as heliodor, which translated from the Greek name means “gift of the sun”. While it is ideally described as a golden yellow, the color range goes from greenish yellow to orange yellow. It is not always brightly colored and can have a muddy, brownish saturation.
Range of Heliodor Colors
Heliodor is pleochroic, meaning it shows different colors at different angles. While faint, it primarily shows two colors ranging from brownish yellow to bright yellow. Splitting the light in two directions means it is dichroic. Its hardness is around 7.5 to 8 on the Mohs hardness scale, meaning it is resistant to knicks and scratches.
The sole difference between emeralds and heliodor is that emeralds are colored by chromium and vanadium, while heliodor is colored by iron. Aquamarines, the blue variety of beryl, are colored by iron too but the iron is charged differently.
One of the few differences between heliodor and emeralds is that heliodor is a Type I gem and Emerald is a Type III. The different types refer to different standard clarity. Type I gems are typically clear, Type II gems often have some inclusions, and Type III gems are expected to be included. Clarity is judged differently for each type depending on what should be expected of its crystal formation.
Due to the high demand for clarity in gems and how scarce this is in emeralds, particularly clear ones go for a premium.
Unsurprisingly, one of the main sources for heliodor is Brazil, one of the primary world-wide emerald suppliers after Colombia. There are other suppliers like Russia, Ukraine, Madagascar, and Namibia. Most of these sources also produce other colors of beryl. For example; if an area produces heliodor, the odds are good that there is an aquamarine pocket nearby since they are the same mineral species and colored by the same element.
Heliodor is capable of producing the cat’s eye phenomena, just like emeralds are. They do not normally produce other phenomena, or effects, barring one-in-a-million exceptions.
Heliodor is frequently used in jewelry, but does not go for high prices due to the low saturation the yellow color normally shows. Demand is never high for gems that display muddy colors, with gems that can show vivid yellows like yellow sapphires instead proving to be much more popular.