Hiddenite is a variety of spodumene, which is defined by its yellowish and/or greenish color. This coloration results from the presence of chromium within the spodumene structure. However, because spodumene crystals are strongly pleochroic, the observed hue will depend on the stone's orientation or the angle from which it is viewed.
The gemstone has a relatively short history, having been discovered by W. E. Hidden towards the end of the nineteenth century in Alexander County, North Carolina. This deposit continues to be a key hiddenite source, but gem-quality material has also since been found in Afghanistan, Madagascar and Brazil.
It should be noted that some purple or lilac kunzites will turn green when irradiated. However, this material is not hiddenite, and the green coloration fades very quickly upon exposure to light.