Rafts

Rafts are thin, sheet-like deposits that form on cave pools. They form when mineral-laden dripwater hits a pool surface, spreading out and depositing its mineral content as a thin crust. Photos 1 and 2 show very thin films of calcite floating on a pool. As these thicken, they often sink to the bottom. Photo 3 shows a very unusual scenario, a small pool that is one giant raft sheet on part of it and grades into more fractured pieces of raft…likely due to drips from the ceiling or stalactites above it. Photos 4 and 5 show large rafts in now-dry pool basins, in one case without and the second case with, pool spar lining the bottom.

In some cases, rafts may also “glue” themselves to the side of the pool edge, as seen in photo #6. This shows the edge of a large, now-dry pool basin, which was stained orange from iron impurities in the calcite deposited in the inside of the pool as mammilaries.

In Lechuguilla Cave, New Mexico, deposits of rafts several feet thick are found in old pool basins. Sometimes these pile up and form raft cone stalagmites.