This is the formula for pure Sphalerite. In some localities, it contains cadmium, indium, and gallium.
Some specimens contain crystals of different colors, and there is a brown, globular, banded variety.
Streak Pure Sphalerite has a white streak. However, impurities are almost always present, giving this mineral a light brown streak. The streak is always a lighter color than the specimen. Most commonly as tetrahedral crystals, which are usually twinned and grouped together. They may closely resemble octahedral crystals.