Boxwork consists of a network of thin blades of crystalline material protruding from bedrock walls, ceilings, or clay floors. The material is generally more resistant than the host rock, and is typically calcite. Probably the most extensive boxwork deposits known are in Wind Cave National Park in South Dakota (Photo #1). The second image shows Dr. Hazel Barton with a ceiling densely covered with large blades of boxwork, many of them caked from mud left by former stands of the lake beneath it, which varies seasonally with fluctuations of the local water table. In the third photo (also from Black Chasm Cavern, California) we see unusually large boxwork “sheets” extending from the walls that are so paper-thin as to be translucent to a flash positioned behind them. Much of the largest one has had so much material dissolved that it forms a lacework, probably associated with seasonal water fluctuations that inundate it.
One way boxwork may form is by calcite filling veins in the bedrock, which later dissolves away to leave the more resistant calcite. This would occur during the phreatic phase, when the cave is filled with water. Another type of boxwork may occur as a more traditional speleothem, in air-filled caves. In this view, calcite solutions seep into shallow cracks and deposit as for other speleothem forms, by degassing of carbon dioxide.
AUTHOR: Dave Bunnell