This is beautiful cluster of gleaming pyrite crystals. It comes from the Huanzala Mine in Peru and the entire specimen measures 2" across.
The mineral pyrite or iron pyrite is commonly referred to as Fool's Gold because its 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, including cubes of all sizes, penetration twin cubes, pyritohedral clusters and as small druzy crystals that can exhibit a beautiful glistening effect.
Nodules of pyrite have been found in prehistoric burial mounds, which suggests their use as a means of producing fire. Wheel-lock guns, in which a spring-driven serrated wheel rotated against a piece of pyrite, were used before development of the flintlock.