Mineral Family: Sorosilicates

Chemical Composition: Ca2Al3 (SiO4)3(OH)
Cleavage: Perfect
Color: Green, yellow-green, white/grey
Crystal System: Orthorhombic
Form/Habit: Prismatic
Fracture: Conchoidal to uneven, brittle
Gravity: 3.2-3.4
Hardness: 6-7
Luminescence: Orangey-yellow (long wave)
Luster: Vitreous
Streak: White
Transparency: Translucent to Opaque

Where is Zoisite found?

Zoisite Placeholder

Zoisite is found in several places around the world.

  • Blue/purple Zoisite, “Tanzanite” – Tanzania, also Pakistan, United States
  • Green Zoisite (often associated with Ruby) – Tanzania
  • Pink Zoisite “Thulite” – Norway, South Africa, United States

What is Zoisite?

Zoisite is a Silicate mineral. Silicate minerals form 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. Zoisite belongs to the sorosilicate family, in which two tetrahedral groups share a single oxygen molecule. It is closely related to Danburite, Epidote and Vesuvianite.

How is Zoisite formed?

Zoisite is formed by regional metamorphism and by the hydrothermal alteration of igneous rocks. It is sometimes found in Quartz veins and pegmites.  Thulite gets its pink coloring from manganese-rich variety of Zoisite.  Tanzanite’s coloring is due to heat, rather than an element.

How is Zoisite mined?

Zoisite is mined in its primary deposit and may be found near Ruby, Jade or other gemstones. The most valuable type of Zoisite is the blue/purple gemstone Tanzanite, found only in Tanzania where it is primary purpose of artisanal and small-scale mines.

Zoisite Enhancements

Green Zoisite and pink Thulite are natural stones, enhanced only through cutting and polishing.  Blue-purple Tanzanite can be natural, but is often heat-treated to bring out a more vivid shade.  In nature, Tanzanite gets its coloring from the heat from grassfires.

Mereni Hills

View of Mount Kilimanjaro from the Zoisite Mines (Tanzanite), Mererni Hills, Northern Tanzania.