Sphalerite

Two samples with one yellow and the other brown to black. Rounded tetrahedral and dodecahedral faces. Vitreous lustre. Sphalerite (ZnS) can be yellow, brown, red, green, black, white (rare) or pale grey (Cleiophane). Lustre can be resinous, adamantine or submetallic and streak is light brown that will always be lighter in colour than the sample. Hardness is 3 1/2 to 4 and cleavage is perfect in six directions. Sphalerite usually occurs as tetrahedral and dodecahedral crystals with rounded crystal faces but can also be cleavage masses or granular, compact and botryoidal.