Page 14 - Curriculum Visions Dynamic Book

Caves and caverns
Calcium-containing materials are precipitated in many forms in caves and passages underground. They may form sheets of stone that mask the cave walls, rising columns called stalagmites,
or descending columns called stalactites. However, each is made as water laden with calcium carbonate seeps into the caves.
How water becomes rock
The calcium in hard water cannot be seen as
it percolates out of tiny cracks in the walls and roofs of the cave. The water looks entirely clear. This is because the calcium is contained as calcium bicarbonate, a transparent solution.
As the water enters the cave, some of the dissolved carbon dioxide escapes, and as a result calcium carbonate is precipitated as tiny crystals of calcite, known as travertine. Over time these build into the fantastic forms inside some caves.
Cave formations
The shape that grows depends on the way the water drips from the roof and walls. If it drains over the walls, then curtain stalactites or flowstone curtains will form. But if it drips vertically, then stalactites will form on the roof of the cave, and stalagmites will form directly below, at the point where the water drips onto the floor.
Stalactites are not solid but rather consist of conical
tubes. The water flows down the center of each tube and deposits more crystals on the outside edges of the drip. Stalagmites are
thicker and more rounded in shape than stalactites and are solid rather than hollow.
The chemical precipitation takes place very slowly. In fact, it is uncommon for a stalactite to grow at rate greater than 2 mm a year. Stalactites that are many meters long are therefore very old.
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