The in the form of fossilized shells.

The best adventure movies always seem to include a scene in a cave. Caves are also fascinating from a scientific standpoint. In this lesson, you will learn about chemical sedimentary rock and how it relates to caves.

What is Chemical Sedimentary Rock?

Some of the world’s most beautiful sites are composed of sedimentary rock.

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Think of the Grand Canyon in the western United States. Winding across the continent, it has layers of rock that extend farther than the eye can see and is truly beautiful to behold. It is somewhat hard to believe that this amazing natural landform is made entirely of sedimentary rock. Sedimentary rock is simply any rock that is composed of sediments (bits of rock and other earth material) that have been cemented (glued) together.

Some sedimentary rock starts off as a solution of water and sediments. Sometimes, the sediments are even dissolved in the solution before the rock forms. Any sedimentary rock that forms, as sediments settle out of a solution, is called a chemical sedimentary rock. Sediments can settle out of a solution either by the liquid in the solution evaporating, or by too much of the sediment dissolving in the solution (called supersaturation). When supersaturation occurs, the sediment forms chemical sedimentary rock naturally.

Chemical Sedimentary Rock and Caves

Caves within the Earth are quite often formed as water erodes away material. Certain rock types are very easily eroded by water. One of these types is called limestone. Limestone is very easily dissolved by water. As limestone dissolves, the solution that forms will often find its way into other cave systems, dripping through the ceiling. These slow, constant drips are what lead to stalactites (hanging from the ceiling) and stalagmites (rising from the ground). It is very similar to how icicles form, but instead of water freezing, dissolved limestone is coming out of the solution and being left behind on the tips of the stalactites and stalagmites.

Stalactites and stalagmites. As limestone solution drips from the ceiling of caves, small amounts of limestone will come out of the solution and form these structures very slowly.
This chunk of limestone shows evidence of marine lifeforms in the form of fossilized shells.
Halite, commonly known as rock salt, forms as the water in the original solution evaporates.

Gypsum: Another evaporite, gypsum is also among the most common types of chemical sedimentary rock. It is commonly used in fertilizer and as a main ingredient in classroom chalk.

Gypsum forms much in the same way as halite and is, therefore, also an evaporite.

Lesson Summary

A special type of sedimentary rock, chemical sedimentary rocks form as sediments settle out of a solution.

It is common for caves within the Earth to be formed of chemical sedimentary rocks. Evaporites, a special type of chemical sedimentary rock that include halite and gypsum, form as sediments, and are left behind when water in the original solution evaporates.


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