Natural. Not treated.
Grandidierite is a very rare mineral that was first discovered in southern Madagascar in the early 20th century. Since grandidierite is quite hard, high quality material has been cut as gemstones, making it one of the very rarest gems.
Gemologically, grandidierite is a magnesium aluminum borosilicate. It has a hardness of 7 to 7.5 on the Mohs scale, similar to garnet; a density of 2.85 to 3.00, in the approximate range of tourmaline; and a refractive index of 1.590-1.623.
It forms in the orthorhombic crystal system. Grandidierite is typically bluish green in color and derives its distinctive color from traces of iron. Gemmy material is translucent to transparent. Fully transparent specimens are ultra rare.