Wiluite

Wiluite is a dark green, brownish, or black blocky silicate mineral with formula: Ca₁₉(Al,Mg,Fe,Ti)₁₃(B,Al,[ ])₅Si₁₈O₆₈(O,OH)₁₀. It has a Mohs hardness of 6 and a specific gravity of 3.36. It has a vitreous lustre, poor cleavage and an irregular brittle fracture. It crystallizes in the tetragonal system and occurs as well-formed crystals with good external form. It is isostructural with the vesuvianite group and is associated with wollastonite and olive-green grossulars (viluites) in a serpentinized skarn.