Pyrite, sometimes called fool’s gold is a compound of iron and sulfur. Depending upon the conditions under which it forms pyrite can form crystals of different shapes, cubes are common. Pyrite is used in making sulfuric acid. Pyrite can be an agent of fossilization creating beautiful fossils, commonly ammonites and brachiopods. In the gold rush era, many people thought they had discovered gold only to realize it was pyrite, which is where it gets its nickname fools gold. Hardness 6-6.5 Metallic luster