This sample combines crystals of the minerals pyrite and quartz. Pyrite is an iron sulphide (FeS2), a widespread mineral that is found in many types of rock. It fits the cubic crystal system, and well-developed crystals of pyrite form perfect cubes (hexaeders) with smooth or striated metallic surfaces. The glossy grains in freshly broken rock can be mistaken for gold and and so it is also known as "fool's gold". In this sample the pyrite is interspersed with milky-white crystals of quartz, 6-sided prisms ending in a 6-sided pyramid, a typical habitat for quartz crystals. Quartz is composed of silica (SiO2) and is one of the most common rock-forming minerals of the Earth's crust. From the Buenaventura mine in the Pasto Bueno mining district, Peru. Actual width of sample is 160 mm.