| Prasiolite | |
|---|---|
 Natural prasiolite from Różana, Nowy Kościół, Lower Silesian Voivodeship, Poland | |
| General | |
| Category | Tectosilicate minerals |
| Group | Quartz group |
| Variety of | Quartz |
| Crystal system | Trigonal |
| Identification | |
| Color | Shades of green |
| Crystal habit | Hexagonal prisms |
| Cleavage | None |
| Fracture | Conchoidal [1] |
| Tenacity | Brittle [1] |
| Mohs scale hardness | 7 – lower in impure varieties [1] |
| Diaphaneity | Transparent |
| Specific gravity | 2.65 |
| Refractive index | 1.544 to 1.553 [2] |
| Birefringence | 0.009 [3] |
| Ultraviolet fluorescence | None |
Prasiolite (also known as green amethyst or vermarine) is a green, transparent variety of quartz that derives its color from the presence of Fe2+ ions within the crystal structure. [1] [4] Prasiolite is not the only green variety of quartz, and it should not be confused with prase, chrysoprase, chrome chalcedony, or quartz colored by inclusions of chlorite or epidote.
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Natural prasiolite is exceedingly rare, having been first discovered in the early 19th century in Lower Silesia, Poland [5] [6] with only a few other deposits known to exist. Natural prasiolite deposits include Płóczki Górne (Poland), Bahia (Brazil), Thunder Bay (Canada), and Farm Rooisand (Namibia). [6]
Nearly all commercially available prasiolite is artificial, either produced by heat-treating amethysts from certain locations [7] to 400-500 °C, [8] or irradiating yellow-tinged quartzes. [9] Most amethyst will turn yellow or orange when heated, producing heat-treated amethysts which are often marketed as citrine, but some amethyst will turn green when treated. [8] Significant prasiolite production began in the mid-1950s with the discovery that amethysts from the Montezuma mine in Minas Gerais, Brazil turned green when heat-treated. [10]
Most prasiolite sold is used in jewellery settings, where it can substitute for far more expensive gemstones, such as peridot, tsavorite, and emerald. [11] Prasiolite used for jewelry comes from two main sources: heat-treated amethyst from the Montezuma mine, and irradiated yellow-tinged quartz from various locations throughout Brazil. [4]
Prasiolite is sometimes incorrectly called green amethyst, [12] which is not an acceptable name for the material according to Federal Trade Commission Guidelines. [13] Other names for green quartz include vermarine and lime citrine. [14]
The word prasiolite literally means "leek-green stone" and is derived from Ancient Greek πράσον prason meaning "leek" and λίθος lithos meaning "stone". [15] [16] The stone was given its name due to its green-colored appearance.
Natural prasiolite is often a very light, translucent green. Darker green quartz is generally the result of artificial treatment, [17] [ dubious – discuss ] with lighter-colored prasiolite often irradiated with gamma rays as an attempt to obtain deeper colors. [18]
