Prasiolite

Mineralogy of Prasiolite

Mineral Family: Tectosilicate

Chemical Composition: SiO₂ 
Cleavage: None
Color: Green
Crystal System: Hexagonal/trigonal
Form/Habit: Prismatic
Fracture: Conchoidal, very brittle
Gravity: 2.65
Hardness: 7
Luminescence: None
Luster: Vitreous
Streak: White
Transparency: Transparent to translucent

Location: The most important Prasiolite deposits are in Brazil. Additional Prasiolite deposits are located in Canada and Poland.

Mineral Family: Prasiolite is the green variety of Quartz, which is in turn a Silicate mineral. Silicate minerals are the largest family of minerals, including more than 25% of all known minerals and 40% of all common minerals. In addition to being a major part of the Earth’s crust, Silicate minerals have also been found on the moon and in meteorites. Silicates are minerals which contain the elements Silicon (a light gray, shiny metal) and Oxygen (a colorless gas). Together, these two elements form a tetrahedron – a shape similar to a pyramid – with a Silicon atom in the center and Oxygen atoms at each of the four corners. These tetrahedra connect with other chemical structures, in six different ways, to form various minerals and rocks. There are six main groups of Silicate minerals, and these main groups are further subdivided into secondary subdivisions, such as Quartz and Feldspar. Quartz is a large mineral family in its own right and its members come in every shade of the rainbow. Colorless Quartz is called Clear Quartz or Rock Crystal. Yellow Quartz is Citrine. Green Quartz is Prasiolite. Brown Quartz is Smoky Quartz. Pink Quartz is, of course, Rose Quartz. The most highly prized variety of all is Amethyst, or purple Quartz. While Amethyst ranges from light violet to darkest purple, transparent crystals with a deep, rich, royal purple color are the most desirable.

Formation: Prasiolite is created when liquid magma from a volcanic explosion cools down and transforms into igneous rocks. During this cooling down period, silica acid bubbles shift from being a gas/liquid into a solid compound. The bubble becomes a hollow space in the igneous rock and the silica acid becomes Quartz crystals. Trace particles of iron within the silica acid give Prasiolite its green color, otherwise the silica acid would transform into Clear Quartz. The temperature at which the Quartz cools down determines the color, which can either be green, purple (Amethyst), or yellow (Citrine).  

Mining: Natural Prasiolite is very rare, when it is found it is almost always as a secondary mineral within commercial Amethyst mines.

Enhancements: While Prasiolite does occur naturally, the vast majority of Prasiolites are heat-treated Amethysts. More than 200 years ago, it was discovered that when Amethyst and Smoky Quartz are carefully heated, they change color. This discovery gave mines and gem dealers a a way to transform low grade Amethyst and Smoky Quartz into a more desirable commodity. Usually Amethyst turns yellow when heated, becoming Citrine, in part due to the formation of iron oxides. Iron compounds with Fe³⁺ ions are often yellow or orange, whereas Fe²⁺ compounds are green. Today only a trained specialist can recognize the difference between burnt Prasiolites, which have subtle stripes, and natural Prasiolites which are slightly cloudy. On a chemical level there is no difference between natural and burnt Prasiolite, it is merely a matter of whether nature or man is responsible for the hot temperature. The vast majority of Prasiolite sold on the market is burnt.

Synonyms: Green Quartz, Vermarine, Lime Citrine, Green Amethyst (it is against the Federal Trade Commission Guidelines to call Prasiolite “green amethyst,” nevertheless the practice is very common)

Map courtesy of TravelBlog
Photos: Raw Prasiolite