Published: What Caused the Dinosaur Extinction?

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Published: Are Fossils the Window to the Past

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All About Rocks and Minerals

 

 

Rocks are made up of one or more minerals. Minerals are inorganic (they were never alive) and have an internal structure and chemical composition. These are the solid materials that make up the layers of the Earth. Minerals grow in specific geologic environments ranging from deep within the Earth (higher temperatures and pressures), to near the surface (lower temperatures and pressures). Each mineral has a distinctive set of chemical and physical properties that makes it unique. 

There are three major rock types: igneous, metamorphic, and sedimentary. Igneous rocks, such as granite or basalt, form as a result of a magma (molten rock) that has cooled to form a variety of interlocking crystals. Erosion and weathering cause sediment in rivers and beaches, which over time, can build up and become cemented and compacted to form sedimentary rocks, such as sandstone. Another type of sedimentary rock is limestone, which is made up of small calcite particles formed by marine organisms that build up large reefs in the oceans. Metamorphic rocks form due to changes in the temperature and pressure resulting from a changing geologic environment. For example, if limestone undergoes an intense amount of heat, it becomes the metamorphic rock, marble.

Collections usually differ depending on where the collector is able to search for rocks. In the great interior plains and lowlands of the United States, a wide variety of sedimentary rocks are exposed. Igneous and metamorphic rocks are widespread in the mountains and piedmont areas of New England, the Appalachians, the Western Cordillera, and scattered interior hill lands; igneous rocks make up almost all the land of Hawaii. Along the Atlantic and Gulf Coastal Plains, loose and unconsolidated rocks are widespread; in the northern United States, glaciers deposited many other unconsolidated rocks.

The best-collecting sites are quarries, road cuts or natural cliffs, and outcrops. Open fields and level country are poor places to find rock exposures. Hills and steep slopes are better sites. Almost any exposure of rock provides some collection opportunities, but fresh, unweathered outcrops or manmade excavations offer the best locations. If possible, visit several exposures of the same rock to be sure a representative sample is selected.

A good rock collection consists of selected, representative, properly labeled specimens. The collection can be as large or as small as its owner wishes. An active collection constantly improves as specimens are added or as poor specimens are replaced by better ones. A rock collection might begin with stones picked up from the ground near your home. These stones may have limited variety and can be replaced later by better specimens. Nevertheless, this first step is helpful in training the eye to see diagnostic features of rocks (features by which rocks can be differentiated). As you become more familiar with collecting methods and with geology, the collection will probably take one of two directions. You may try either to collect as many different types of igneous, sedimentary, and metamorphic rocks as possible or to collect all the related kinds of rocks from your own particular area.

See our page The Relic Room for more information about what you can find in Sevierville, TN.