Xilingolite

Xilingolite is a lead sulfide mineral with formula Pb₃Bi₂S₆. It has a hardness of 3, a metallic luster, and usually exhibits a lead-grey color. It is a dimorph of lillianite, exhibiting increased Pb-Bi order and decreased symmetry.

Its crystal system is monoclinic, with three axes of unequal length two of which are at an oblique angle to each other while the third axis is perpendicular to the plane formed by the other two. Xilingolite is opaque, meaning that its internal structure does not allow for light to be transmitted through it. The mineral also exhibits white to blue-tinted-white pleochroism under reflected light.