Salt Flats at Death Valley, California
The Surface of the Earth
Chemical sedimentary rocks form at the earth's surface. Sedimentary rocks are rocks that have been placed by weathering or erosion in layers or beds. Over time, these layers are compressed and cemented together. Add more time to the process, and these rocks break apart into smaller pieces. Chemical sedimentary rocks differ from other sedimentary rocks because they are decomposed at the surface of the earth. Chemical processes affect and control the formations of these layers of rocks.
Water Transports Minerals
Rocks are made up of minerals. Water in the form of rivers, streams and rain travels through existing rock layers and causes the minerals in the rocks to dissolve. Water breaks down the original rock with a chemical reaction that causes the minerals to dissolve into a solution that is readily transported in water. The minerals are then carried away with the water. As stated in the above step, this usually occurs at the surface of the earth although underground streams and rivers can also rinse rocks and remove minerals.
Water is an erosion agent. Any type of water can act in this manner to remove minerals from rocks. Seawater, rain, rivers and streams all are capable of transporting mineral deposits. In addition, air can sometimes move fine particles of minerals and deposit them in another location.
Remember that the method of transport must have enough force to actually keep the minerals in suspension. If the water flow is too light, the minerals will simply be released to drop to the bottom of the river or stream.
Mineral Deposits
Minerals that are carried away by the water must end up somewhere. As the water evaporates, these minerals become deposits that form the typical layering seen in sedimentary rocks. Over thousands of years, layers form as subsequent deposits of minerals are made in the same location. Compression by the newer deposits forms layers of mineral deposits. The weigh of the upper layers cements the lower layers, forming a solid rock.
Chemical sedimentary rocks are identified by the minerals that make up the rock itself. In many cases, it's possible to tell where the sedimentary rock has come from by identifying the minerals it contains. Layers are not always horizontal. If there are long periods of time between depositions of minerals, the deposition site can be eroded by weathering. In this case, layering beds may run in different directions. However, you will still be able to see the layered bedding of the rock.
Evaporation
Chemical sedimentary rocks are particularly susceptible to the whims of the water. Because the method of transport keeps the minerals intact for deposition at a layering site, quick evaporation of the water can greatly affect the type of chemical sedimentary rock that is formed. A good example of evaporation affecting a chemical sedimentary rock is rock salt. Minerals are dissolved from other rocks and transported to a deposition site. The water evaporates quickly and forms mineral rock salt. We use this every day in the form of table salt. This type of evaporated chemical sedimentary rock typically occurs near dry lake beds and inland seas.
Tags: sedimentary rock, chemical sedimentary rock, Chemical sedimentary rocks, sedimentary rocks, carried away, causes minerals
