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The Mineral boracite

Intergrown Cubic Boracite Crystal

Boracite describes both a mineral group as well as an individual mineral within that group. The Boracite group is a solid solution series of chloro-borates, with Boracite, Chambersite, and Ericaite, as the main members. Boracite is the magnesium-rich end member, and the most prevalent mineral of this group.

Boracite is known for its equidimensional crystals, which may form in unique habits not seen elsewhere in the mineral kingdom. Up until recently, Boracite crystals were generally isolated small crystals, but a find in the Boulby Mine in England has produced large crystal groups much different then previous discoveries of this mineral. Boracite is named after its membership within the borate group, containing the element boron in its chemical composition.

Chemical Formula

Mg₃B₇O₁₃Cl

Color

Colorless, light blue, green, grayish-green, sea-green. Rarely red, pink, or yellow.

Crystal System

Orthorhombic

Properties

Streak
White

Hardness
7 - 7.5

Transparency
Transparent to translucent

Specific Gravity
2.9 - 3.0

Luster
Adamantine, vitreous

Cleavage
None

Fracture
Uneven

Tenacity
Brittle

Other ID Marks
Weak greenish fluorescence in shortwave ultraviolet light.

Crystal Habits

Crystals are in cubic, dodecahedral, or tetrahedral habit, often with modifications. Crystals convert to an orthorhombic crystal structure upon cooling after their formation, though the isometric shape is preserved. Crystals may be in individual floater crystals, as well as in groups of crystals.

3D Crystal Atlas

Additional Information

Composition
Magnesium chloro-borate, sometimes with iron and manganese

In Group
Borates; Anhydrous Borates

Striking Features
Crystal habits, hardness, and mode of occurrence

Environment
In marine evaporite deposits including salt domes.

Rock Type
Sedimentary

Varieties

Stassfurtite

- A fibrous variety of Boracite from the potash deposits of Stassfurt, Germany.

Uses

Boracite is a rare collector's mineral, and small crystals make highly collectible specimens for thumbnail collectors.

Noteworthy Localities

A classic locality for Boracite crystals, in green and grayish-green equidimensional crystals, is the potash deposits of Bernburg and Stassfurt in Saxony-Anhalt, Germany. Single floater crystals, in dodecahedral or modified cubic form, have come from from Lüneburger, Niedersachsen (Lower Saxony), Germany. Transparent green Boracite crystals, mostly in tetrahedral form, have come from the Glückauf Mine, Sondershausen, Thuringia, Germany.

A more recent find of Boracite is at the Boulby Mine, Loftus, North Yorkshire, England. This locality has produced sea-green crystals, in large clusters many times larger than all previous finds of this mineral. Another recent and important producer of Boracite is Alto Chapare, Cochabamba Department, Bolivia. Crystals from this mine are in cubic form with poor transparency, and usually in matrix. The color ranges from grayish-green to a less common peachy pink.