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How to Recognize Limestone

Made up of the fossilized shells and skeletons of tiny, ancient animals, the limestone rock present today is a result of hundreds of millions of years of formation. Limestone is considered useful for construction purposes, and is often used to form the foundations of buildings. Because limestone rock is easily dissolved by mineral water, limestone-walled caves are revealed when the water table begins to recede. For this reason, caves can often be found in areas rich in this type of sedimentary rock. Although it can appear similar to other types of rock, such as marble, there are several methods used to help correctly identify limestone.

Things You'll Need

Knife
Vinegar
Microscope or magnifying glass

Instructions

- 1
  Observe the texture of the rock. Limestone is smooth, with almost no holes in its surface. In contrast, slag rock has many small holes throughout.
- 2
  Scratch the rock with a knife. If white powder results from the scratch, the rock is softer than the knife. If the knife appears to be scratched by the rock, the rock is harder than the knife. Limestone, as well as dolostone, can be easily scratched. Chert is an example of a stone that is harder than a knife.
- 3
  Pour a drop of vinegar onto the rock you are trying to identify. If the vinegar produces bubbles accompanied by a fizzy sound, your rock is most likely limestone. This reaction occurs due to vinegar coming into contact with the calcite in the limestone rock. Marble is the only other type of rock that will react with vinegar.
- 4
  Place a fragment of the rock under a magnifying glass or microscope. Limestone appears grainy in appearance when magnified, whereas marble does not. Often, small fossils can be found when limestone is magnified.

Rocks & Minerals