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.
Suggested
reading:
- Lane,
E., 1987, A guide to rocks and minerals of Florida;
Florida Geological Survey Special Publication 8
(revised), 61 p.
