Pirite (FeS2, iron disulfide) from Manresa. Pyrite crystallizes in the regular system, in cubes and pentagonal dodecahedrons of yellow brass color. The hardness of pyrite is 6 –it cannot be grated with a knife but with a quartz crystal-. In Bages, pyrite is found in gray mudstones stratums of marine origin. The crystal size usually is less than 4 millimeters. Often, pyrite builds aggregates that refill ancient galleries that were opened by marines invertebrates –the so-called burrows-. One of the world most important deposit of pyrite is located in Río Tinto (Huelva). Pyrite is exploited mainly to manufacture sulfuric acid and also as a source of iron. [photo Joaquim Sanz / Museum of Geology Valentí Masachs]