Mammilaries or cave clouds are carbonate coatings that form underwater in cave pools whose water is super-saturated with calcium carbonate. They most likely form below the water table, in the phreatic zone, rather than in perched cave pools. They form in concretional layers around projections and rocks lining the pool. In the top photo, clouds have formed in what is now a partially dry pool basin (the caver is holding a dipper for collecting water from it). The floor is littered with dry calcite rafts. The orange staining is due to iron-rich minerals that were in the partially drained basin as it stood static for hundreds or thousands of years. In cross-section, mammilaries show rings much like in a tree or a stalagmite, as shown in the middle photo where a broken piece was observed. In the bottom photo, we see a cloud dipping into a pool I explored with SCUBA gear. All 3 photos are from Lechuguilla Cave, New Mexico, where clouds are common in lower levels.