Boracite - Encyclopedia

    Class : Carbonates, nitrates, borates
    Subclass : Borates
    Crystal system : Orthorhombic
    Chemistry : Mg3B7O13Cl
    Rarity : Uncommon


Boracite is a mineral that crystallizes in the cubic system above 265°C ; below it becomes orthorhombic while maintaining cubic forms. Magnesium can be partially replaced by iron (ericaite variety) or manganese (chambersite variety). It owes its name to the boron it contains. Boracite is present in beds in ancient evaporite deposits, especially in the German Permian, associated with anhydrite, gypsum, halite (Lüneburg), kainite and carnallite (Stassfurt) and in saliferous diapirs. American (Louisiana and Mississippi). It comes from the light metamorphism of hydrated borates. The crystals are generally millimetric and display cubic forms or derived from the cube : dodecahedron, cubo-octahedron, tetrahedron. Boracite is sometimes massive, saccharoid, resembling a fine-grained white marble, but much harder. It is usually colorless or tending towards gray, yellow or green. Boracite is highly piezoelectric. It is an exceptionally boron ore and has sometimes been cut for jewelery. It is a mineral little known to collectors.

Boracite in the World

The most beautiful crystals of boracite are characteristic of German Permian salt deposits in the region of Stassfurt (Saxony-Anhalt) : Lüneburg, Eime, Wathlingen... The transparent crystals of a superb blue-green reach the 15 mm in size on a matrix of gypsum and anhydrite. The other localities did not deliver beautiful crystals even though the boracite can be abundant : Aislaby (England), Inowroclow (Poland), Choktow (Louisiana).

Boracite in France

Boracite is not present in the French underground.

Twinning

A boracite twinning on (111) exists but is very rare.

Fakes and scams

No fake inventories for this mineral species. Some crystals could be glued on matrix...



Hardness : 7 to 7.5
Density : 2.91 to 3.1
Fracture : Irregular to conchoidal
Trace : White



TP : Translucent to transparent
RI : 1.658 to 1.673
Birefringence : 0,010 to 0,011
Optical character : Biaxial +
Pleochroism : Very weak
Fluorescence : None


Solubility : water, hydrochloric acids

Magnetism : None
Radioactivity : None