Mineral crystals are made as the shallow water that has flooded the bottom of Death Valley evaporates.
Click on image for full size
Courtesy of Martin Miller, University of Oregon

Chemical Sedimentary Rocks

Unlike most other sedimentary rocks, chemical rocks are not made of pieces of sediment. Instead, they have mineral crystals made from elements that are dissolved in water.

The water in the oceans, lakes, and ground is often full of dissolved elements. All sorts of things can dissolve into water. If you put a spoonful of salt into water, the salt will eventually dissolve. Seawater tastes salty mainly because there are salty minerals such as halite dissolved in it.

Sometimes water becomes so full of dissolved elements that they will not all fit. Some are not able to remain dissolved and form solid mineral crystals. This usually happens when some of the water has evaporated away, leaving less room for the dissolved elements. If enough water evaporates, they do not all fit and some form crystals of minerals such as halite, gypsum, and calcite. In the picture to the left, minerals are forming out of shallow water that has flooded the bottom of Death Valley in California. The valley is so hot and dry that water evaporates very quickly, leaving behind the minerals that were once dissolved in it.

Last modified August 25, 2003 by Lisa Gardiner.

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TES XXVI, 3 fall 2010 The Fall 2010 issue of The Earth Scientist, focuses on rocks and minerals, including articles on minerals and mining, the use of minerals in society, and rare earth minerals, and includes 3 posters!

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