Quartz is one of Tennessee's most common crystal rocks.
A variety of crystal rocks are found in Tennessee, with one of the richest sources being the area around Nashville and Carthage. Tennessee's crystals are prized by collectors and mined by industry. The Elmwood zinc mine, in Carthage, produces crystals of sphalerite, fluorite, barite and calcite of exceptional quality. Tennessee's crystals are found in its sedimentary limestone rock. In some parts of the state, quartz crystals lie loose at the soil's surface.
Silicate Group
Quartz is composed of silica. It is one of the world's commonest crystals. Tennessee quartz is commonly clear rock crystal, though white quartz is also found. Copper mines at Ducktown had quartz floors yielding crystal of unusual form and clarity. Quartz geodes are common around Center Hill Lake and Cannon County. Loose quartz crystals -- field diamonds -- are readily found in Greene County. Douglas Lake is another source of these crystals, known locally as Douglas diamonds.
Sulfide Group -- Metal Ores
Fool's gold is commonly found in quartz rock.
Iron pyrite, or fool's gold, forms small, sparkling crystals in coal seams and on quartz, in the same areas where gold and silver occur. Clumps of dark, lustrous crystals are likely sphalerite (zinc sulfide), a zinc ore. Sphalerite mines are located mainly in East Tennessee, but the largest is the 300-mile expanse of Elmwood mine. Galena (lead sulfide) is a metallic gray, cubic crystal. Galena is a lead ore, found in sedimentary rock, in association with pyrite and sphalerite. Each mineral in this group has sulfur as part of its chemical formula. Exposed to rainwater and oxygen, sulphide minerals bleed sulfuric acid. Streams in the Cumberland plateau have been so damaged by acid drainage from coal mines, that they are declared "dead."
Halide Group
Halides are crystals with a halogen -- fluorine, chlorine, iodine or bromine -- as part of their chemical structure. Fluorite, a component of fluoride toothpaste is common in Tennessee. It is also used in the aluminum and steel industries. Crystals of fluorite are cubic. They are frequently found alongside, or growing on, sphalerite. Fluorite here is a rich, purple-blue color, prized by collectors. Elmwood mines have yielded exceptionally fine fluorite crystals.
Carbonate Group
Calcite is the main component of limestone (calcium carbonate), originally laid down as sediment by warm, shallow seas. Calcite washed from limestone forms stalactites and stalagmites in limestone caves. Large, individual calcite crystals are found in Tennessee's mines and caves. Their color is transparent amber. The shape is a faceted teardrop, or dog's tooth.
Sulfate Group
Gypsum (calcium sulfate dihydrate), barite (barium sulfate) and celestite (strontium sulfate) form clusters and rosettes of rod- or blade-shaped crystals. Gypsum crystals may be transparent, but in Tennessee are usually white. A natural insulator, gypsum feels warm to the touch. Gypsum is mined to make cement and wallboard. Barite and celestite are often found together. Celestite, a sky blue, appears like shards of ice or broken glass. Where deposits are large, celestite is mined for strontium, used in fireworks and colorants. Barite is honey-colored and at Carthage is found in ball formations, resembling dirty snowballs. A heavy crystal, barite is used in the oil industry to prevent "blow outs" during drilling. Barite also is used as a filler in paper and in medicine for barium enemas.
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