Prasiolite

Prasiolite (also known as green quartz, green amethyst or vermarine) is a green variety of quartz, with its color typically coming from Fe²⁺ ions within the crystal structure.^[1][4]

Not to be confused with Praseolite.

Prasiolite
General
Category	Tectosilicates, quartz variety
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 to nearly opaque
Specific gravity	2.65
Refractive index	1.544 to 1.553[2]
Birefringence	0.009[3]
Ultraviolet fluorescence	None

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]

Green quartz 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 a very light, translucent green. Darker green quartz is generally the result of artificial treatment,^[17] with lighter-colored prasiolite often irradiated with gamma rays as an attempt to obtain deeper colors.^[18]

See also

• List of minerals