SciShow Rocks Box: Aragonite

Locality: Santa Eulalia, Chihuahua, Mexico Chemical Formula: CaCO3 Mohs Hardness: 4 Aragonite is one of the crystal forms of calcium carbonate, and while we do find it on land in big chunks like the one you’re getting, we also find a whole lot of it in the ocean. It doesn’t grow there on its own. Marine organisms build it out of ions floating around in the water. Aragonite crystals are the building blocks for everything from mollusc shells to coral skeletons to pearls. It’s even found in the shimmery coating of some fossil ammonites called ammolite.