Then it rotates it again 90 degrees and inverts it again through the crystal. The tetrahedral faces of tennantite are in many instances modified by other crystal forms giving the crystals multiple facets while still retaining the overall tetrahedral shape. Most members of the tetrahedrite group belong to this informal group. Although rarer than its cousin, tennantite forms nice crystals and can be a handsome specimen. Often tennantite will contain a certain percentage of silver and be used as a minor ore.
Collectors usually crave nice specimens of verified tennantite.
Color is black to steel gray. Luster is metallic. Transparency crystals are opaque. Twinning is occassionally seen. Also massive and granular.