Florida Geological Survey - Geology Topics
Rocks and Minerals
These are the solid materials that make up the layers of the Earth. Rocks are made up of one or more minerals. 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. All minerals are inorganic (they were never alive) and have an internal order and chemical composition. In Florida, some of the more common minerals include quartz (beach sand), aragonite (shells), calcite and clay minerals such as kaolinite and montmorillonite.
In certain areas of Florida, some minerals are of such economic importance that they are mined. In northeast Florida, for example, a group of minerals known as "heavy minerals" are mined from ancient beach ridges. These minerals, which only comprise a few percent of the total sand, are useful for their titanium (Ti) content. The element Ti is useful for manufacturing paint. In southwest Florida, phosphate minerals are mined for the manufacture of fertilizer products. Florida produces about one-fourth of the world's supply of phosphate.
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. 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. In Florida, sedimentary rocks are the most common. These rocks are made up of cemented mineral particles. One example is shell fragments (the mineral aragonite) that are cemented together by calcite to form the sedimentary rock coquina. Another type of sedimentary rock is limestone, which is mined for road building and other construction applications. This rock is made up of small calcite particles formed by marine organisms that build up large reefs in the oceans. During much of Florida's geologic history, it was covered by the ocean.
Much of the surface of Florida is covered by sediment (loose mineral particles, such as quartz sand), or sedimentary rocks such as limestone and dolostone. Igneous and metamorphic rocks do not occur naturally at the surface, but are found in deep wells reaching from 3,500 feet to deeper than 18,670 feet below land surface.
Last updated: February 09, 2010
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