Cave Pearls, formed as dripping water rich in calcium salts deposits calcite around a small nucleus (often a sand grain). The constant movement of each cave pearl by the dripping water keeps them rounded, with the calcite accumulating evenly and any irregularities being abraded away. If the dripping water splashed less vigorously, a stalagmite would form instead. Peak District National Park, Derbyhsire, UK. January.