Aragonite is calcium carbonate, Ca CO3. It has the same formula as calcite and vaterite, but has a different crystal lattice. Repeated twinning of the crystals produce the pseudo hexagonal crystals as in this specimen . The whole of the surface of this ball is covered with crystals, some with a brown colouration, with no sight of the base rock. The specimen is from an aragonite outcrop in Tazouta, south of Sefrou, Morocco, and is one of many similar specimens from this site.