Grandidierite | blue crystal, rare mineral specimen from MadagascarGrandidierite from Madagascar is a rare and highly sought after borosilicate mineral, best known for its striking blue green to teal coloration. These crystals typically form in pegmatitic environments, and their translucency combined with vitreous luster highlights subtle internal zoning and pleochroism. Madagascar remains the worlds most important source of fine grandidierite, producing some of the best examples known. Size 3. 2 x 1. 7 Cm Weight 10.