This beautiful specimen contains an association of pyrite cubes and sphalerite crystals. It comes from the Huanzala Mine in Peru and the entire piece measures 2.9" across.
Sphalerite is a part of the sulfides group and typically exhibits a grey/black appearance due to high concentrations of impurities. When sphalerite is in it's purest state, the chemical composition is ZnS, and can display a gemmy transparent light tan/yellow color. This is one of the few minerals that can form crystals ranging anywhere between gemmy and transparent to opaque and metallic-like. Opaque or cloudy sphalerite tends to be most abundant, due to the ease of iron replacing zinc in the process of formation.
Pyrite or iron pyrite is commonly referred to as Fool's Gold because it's metallic luster and pale brass-yellow hue give it a superficial resemblance to gold. In the old mining days, Pyrite was sometimes mistaken for Gold. Pyrite is the most common of the sulfide minerals with the chemical formula FeS2. Pyrite crystals occur in many shapes and habits. Smaller (druzy) crystal aggregates may give off a beautiful glistening effects, and larger crystals may be perfectly formed, including fascinating cubes, penetration twins, and other interesting crystal forms.