Some of these minerals belong to the formal group of minerals known as the Fuloppite Group . These minerals are rather similar in characteristics and are difficult to distinguish from one another. Other members of the Fuloppite Group include fuloppite , plagionite , heteromorphite and rayite . Color is gray to black. Luster is metallic.
Crystals are opaque.
Crystal Habits include radial to spherical aggregates of tabular nearly parallel crystals. Cleavage is perfect in several oblique directions. Streak is black. Associated Minerals include quartz , pyrite , stibnite and several other rare sulfosalts.