ceiling, slowly forming stalactites. A livimesto ca usuall often grow and hass t
ID: 118401 • Letter: C
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ceiling, slowly forming stalactites. A livimesto ca usuall often grow and hass to Describe the chemical proc In a develoiving" stalactite is wet, and has a pointed tip where water develo cave, water continues to seep in from the ites often grow upwards from the floor of the cave, 4. Connecting the dots: before falling. Meanwhile, stalagmites a stalactite from water dripping off the stalactite. a. Limestone caves b. Stalactites and stalagmites not? Why do the stalactites have pointed tips while the stalagmites usually do CHEM 1110 Limestone Cave Experiment © Spring 2017 Dr. Sinn Western Michigan University 105Explanation / Answer
a)
Caves form in limestone (calcium carbonate) when water containing dissolved carbon dioxide leaks into rock fissures and joints.
The carbon dioxide forms from the decomposing organic matter in soil, and also comes directly from the atmosphere. This little acidic water dissolves the rock, creates cavities which can enlarge and join up to make bigger cave systems of interrelated chambers. An underground water flow can build up when more rain-fed subsurface drainages join up, or a river can be detained by an open cavity collapse structure and flow underground. This causes additional enlarging of the caves by chemical and physical weathering.
b)
Stalactite and stalagmite are extended forms of various minerals deposited from solution by gradually dripping water. A stalactite hangs like an icicle from the ceiling or sides of a cavern. A stalagmite emerges like a reversed stalactite, rising from the floor of a cavern.
Stalactites are developed by the deposition of calcium carbonate and other minerals, which are precipitated from mineralized water solutions. Limestone is calcium carbonate rock which is dissolved by water that contains carbon dioxide, forming a calcium bicarbonate solution.
This solution moves through the rock until it reaches a boundary and if this is on the roof of a cave it will leak down. When the solution comes into contact with air, the chemical reaction that formed it is reversed and particles of calcium carbonate are formed. This is stalactite. Every stalactite starts with a single drop of water. When the drop falls it deposits the thinnest ring of calcite. Each successive drop that forms and falls deposits another calcite ring. Finally, these rings create a very narrow, hollow tube generally known as soda straw stalactite. Soda straw calcite can develop quite long, but are very brittle. If they become closed by debris, water begins flowing over the outside. It deposits more calcite and creating cone-shaped stalactite.
The water drops that fall from the tip of a stalactite dumps more calcite on the floor below, ultimately resulting in a rounded or cone-shaped stalagmite. Unlike stalactites, stalagmites never begin as hollow soda straws.
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