That reacts with oxygen in the water, forming carbonic acid, which slowly eats away at a mineral called calcite in the limestone, breaking down the rock and eventually creating a hole. When the calcite-rich water makes contact with air inside a forming cave, the carbon dioxide escapes into the air, a little bit like gas fizzing from a newly opened soda bottle. Water seeps through the porous limestone of the cave and drizzles down walls or drips from the ceiling. When the water evaporates, it leaves behind a tiny mineral deposit. Over time, the mineral builds up, creating sheets of rock along walls or rocky spikes that protrude from ceilings.
Minerals carried by drippings that reach the ground can build up into spires.
Sometimes spikes and spires meet one another and grow together into a column. Emerson asked, pointing to a stump in the ground appointed solely for that purpose. He quickly told us not to touch any other formations, as the oil from our hands would prevent calcite in the waterdrops from sticking, stopping any new growth. Isabelle thought the creamy brown walls surrounding us looked like peanut butter, and we discovered that the color comes from iron in the water, which slowly rusts as it runs over the cave wall. Emerson's easygoing nature changed for a moment when he realized someone had thrown in a coin.