Pinalite

Pinalite is a rare lead tungstate–chloride mineral with formula: Pb₃WO₅Cl₂.

Pinalite crystallizes in the orthorhombic crystal system. The orthorhombic system is described as having three crystallographic axes of unequal lengths, normally referred to as c (the longest axes), b (the second longest axes), and a (the smallest axes). These axes all have corresponding angles of 90 degrees. Pinalite belongs to the biaxial optical class, and is negative. The main difference between biaxial and axial crystals is that biaxial crystals have two optic axes.