limestone - hand specimen of limestone with a solution surface - Lower Cambrian Chambless Limestone, Marble Mountains, Calif.

$ 7.50

In arid areas, calcium carbonate limestone and calcium-magnesium carbonate dolomite develop a rough dissolved surface from the action of weak carbonic acid that forms as atmospheric water picks up carbon dioxide. These specimens are excellent examples of that solution surface. Ultimately a karst topography can develop, with solution furrows deep enough to stand in without being able to see over the edge, and with solution of the limestone along underground joints forming caves and sinkholes. The Karst Plateau in Slovenia and Italy exhibits this.

Limestones are cliff-formers in arid regions, forming vista points chosen by countless geology students as a spot to have their lunch. The Madison Limestone in Wyoming, one such rock unit, has been named "The-seat-of-your-pants-formation" from the result of leisurely lunches consumed with feet dangling over the edge. Almost instant tail-end air conditioning.

In humid regions, limestones weather to clay and form valleys instead of cliffs. A good question for your students would be to ask, "Under what type of climate did this form?"  (arid) and then "How do you know?" (the scratchy surface).

The Chambless Limestone, Lower Cambrian in age, weathers to a rough solution surface. Occasionally an algal oncolite - a spherical algal colony ranging up to the size of roughly a quarter, will stand in relief. Dolomite, calcium magnesium carbonate instead of calcium carbonate, will also develop a similar surface in the arid Southwest.

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