Garnet shades of green, beige, brown, gray, and blue, but in incandescent light, they appear a reddish or purplish/pink color. This is the rarest type of garnet. Because of its color-changing quality, this kind of garnet resembles Alexandrite. Andradite is a calcium-iron garnet, CaFe(SiO), is of variable composition and may be red, yellow, brown, green or black. The recognized varieties are topazolite (yellow or green), demantoid (green) and melanite (black). Andradite is found both in deep-seated igneous rocks like syenite as well as serpentines, schists, and crystalline limestone. Demantoid has been called the "emerald of the Urals" from its occurrence there,
Gemstone irradiation enabled the creation of gemstone colors that do not exist or are extremely rare in nature. The term "irradiation" is a very broad one, which covers bombardment by subatomic particles as well as the use of the full range of electromagnetic radiation, including (in order of increasing frequency and decreasing wavelength) infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays. Certain natural gemstone colors, such as blue-to-green colors in diamonds, are the results of the exposure to natural radiation in the earth, which is usually alpha or beta particle. The limited penetrating ability of these particles result in partial