Calcite crystals in layer of flowstone, 8 inches high.
Some speleothems apparently defy gravity. Now and then internal hydrostatic pressure causes secondary formations to project out from others in unusual directions. These are helictites (see illustration on [page 21]). A related form is popcorn (see illustration on [page 22]), the mat of small nodules which coat the “beehive” and other objects in the cave. Also called “cave coral,” popcorn can form under water or along wet walls in response to air currents.
Helictite formed on soda straw
Soft, fibrous mats of calcium carbonate deposited near the surface at Oregon Caves are termed moonmilk. In time moonmilk may harden into popcorn mats. Its manner of formation is not fully understood.
Popcorn in Adam’s Tomb
