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Hard Water Icicles?
In this CSI, we're looking at two types of speleothems. If that's Greek to you well, its Greek to us, too. It means cave deposit. The icicle-shaped mineral deposits that hang down from the ceiling are called stalactites and the cone-shaped wonders that pop up from the cave floor are called stalagmites.
How do these wonders form? Water from the Earth's surface seeps through cracks in the cave's roof. As it drips from the ceiling, the water loses carbon dioxide and deposits a calcite mineral film. New drops of water travel down the hollow center of the deposit to the end of the cone formation. Drop after drop, the stalactites grows in a ringlet formation. Many stalactites start as tubular or "soda straw" stalactites since their diameter is that of a drop of water and their centers are hollow. The large stalactites began as very fragile soda straws and then begin to grow from the outside of the tube as more water accumulates in the cave.
Many stalagmites owe their existence to their drippy friends up above, the stalactites. The stalactites drip water to the floor of the cave where the stalagmites slowly start to grow upward. A column, such as the one pictured here, forms when a stalactite and a stalagmite grow until they join.
Image courtesy of National Park Service.