Limonite is a mineral similar to Goethite, except with some added water. It also is a product of weathering and does not form crystals of its own. However, limonite can replace minerals and form a pseudo-crystaline habit, which is exactly what this specimen represents. This was once a cubic pyrite crystal, but has subsequently erroded to limonite. Interesting, the relic striations on the crystal faces of the pyrite can still be seen. Crystal is approximately 3/4ths of an inch long.