Tennessee State Rock

Limestone

(Calcium carbonate)

Adopted on March 13, 1979

Limestone, Calcium carbonate, found just about everywhere in Tennessee, was declared the official state rock in 1979.

Tennessee marble, as the metamorphic version of limestone is known, is widely used in public and private buildings. In 1969, the General Assembly had given similar status to agate, a cryptocrystalline quartz. This semiprecious gemstone is found only in a few areas of the state. Tennessee marble, as the metamorphic version of limestone is known, is widely used in public and private buildings.

In the building stone industry, any high-quality, hard limestone may be called marble, even if it hasn't metamorphosed to marble. Tennessee's commercial marbles are actually limestones of this type: massive, crystalline, and dense. They occur in beds and lenses within the Holston Formation in the Valley and Ridge physiographic province of eastern Tennessee, a narrow band of folded rocks that date from the Ordovician period (500-440 million years ago). These rocks started out as sediments in shallow seas, over a continental shelf. They come in a variety of colors, from off-white to dark red.

Limestone is a sedimentary rocks made up of layers of silt, small pieces of other rocks, and sometimes the skeletons of tiny creatures. In the middle of the Ordovician period, the first coral reefs appeared. Reefs existed earlier, during the Cambrian, but they were built by sponges and other organisms. The corals joined pre-existing groups of invertebrates, including trilobites, bivalve mollusks (similar to clams and oysters), snails, and cephalopods (mollusks related to today's nautilus, cuttlefish, octopus, and squid). Brachiopods were also abundant and diverse. Brachiopods have bivalve shells, but are not mollusks. The two halves of their shells are not symmetrical. They persist today, but are rare. Most died out during a mass extinction at the end of the Permian period (230 million years ago), when the shallow seas that had covered much of the continents began to retreat. The first fishes had just begun to appear in the Ordovician, but would not dominate the seas until the Silurian and Devonian periods.

In Tennessee, and in much of eastern North America, calcium carbonate sediment accumulated in the warm, shallow continental seas and eventually compacted into limestone. Then, around 300 million years ago, the continents began to converge into the supercontinent Pangaea. The force of the long, slow collision between Africa and North America buckled most of eastern North America into a long, folded ridge, the Appalachians. The Ordovician limestones in eastern Tennessee were pushed into long, narrow, northeast-southwest folds.

Tennessee marble quarrying began in 1838, with a quarry near Rogersville in Hawkins County. Most of the quarries are in the Knoxville area. Tennessee marble is still being quarried and is used for statues, buildings, grave markers, and crushed stone. It is also part of the Lincoln Memorial, Grand Central Station in New York, and the Tennessee State Capitol, among many other buildings and monuments.

There are three basic types of rocks: sedimentary, igneous, and metamorphic.

Sedimentary rocks are made up of layers of silt, small pieces of other rocks, and sometimes the skeletons of tiny creatures. One example of a sedimentary rock is the chalk you use at school. Another example is limestone, one of Tennessee's state rocks. The rocks you see inside caves are made of limestone. The Grand Canyon is made up of sandstone, limestone, and shale that have been eroded by the Colorado River to form the Canyon as it is today.

Igneous rocks started as molten magma or lava and then cooled to become rock. Coarse grained rocks are formed when the lava cools slowly and fine grained rocks from when it cools faster. Some examples of igneous rocks are granite and peridotite. The Hawaiian islands are made of cooled volcanic lava called basalt. One of the most popular igneous rocks is an Apache Tear.

Metamorphic rocks are rocks that have been changed by heat or pressure while forming. Sedimentary and igneous rocks can become metamorphic rock. Slate is used in blackboards, talc in talcum power, and soapstone for carving.
 

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