8.1" Sparkling Cave Calcite (Aragonite) Formation - Potosi Mine, Mexico

Cave calcite is not actually calcite but is formed from aragonite crystals. Calcite and aragonite are both carbonates with the same chemical formula (CaCO3), but different crystal structures and symmetries.

Cave calcite forms underground due to groundwater deposition. While it often forms stalactites and stalagmites it can also form unique, branching, tree-like structures. These beautiful formations are sometimes known as ‘floss ferri’ (flowers of iron) and frostwork.

The massive Potosi Mine at Santa Eulalia produces some really fascinating cave calcite formations. The mine is primarily worked for silver, lead, zinc and copper. A characteristic feature of the ore deposits found within the Cretaceous limestones of Mexico is the presence of caves in close association to the ore.

In 1912 miners broke into the first underground cavern containing amazing cave calcite formations. Additional caverns have been discovered over the decades during mining operations. Luckily collectors have been able to recover some of this material before the caverns are subsequently destroyed by the mining operations.