South Dakota State Stone
Sioux quartzite is a hard, fine-grained, and lustrous metamorphic rock. Traces of iron oxide give it a warm pink color that sets it apart from most quartzites, which tend to be white or pale gray.
A STATE SYMBOL
While South Dakota has not designated an official state stone, Sioux quartzite has had great importance for the state’s history, economy, and culture. This stone underlies perhaps one-fifth of the area of South Dakota and comes to the surface in the southeastern part of the state.
Most notably, it is very much in evidence in the city of Sioux Falls, one of the oldest cities in the state, as well as the largest. An outcrop of Sioux quartzite forms the beautiful Sioux Falls waterfall, which powered the grain mill (made of Sioux quartzite) and later hydroelectric station that gave the city of Sioux Falls its start. Sioux quartzite is still quarried in the vicinity of the city.
Quartzite forms by metamorphism of sandstone. As its name suggests, quartzite is related to quartz; in fact, quartz, sandstone, and quartzite all have the chemical formula SiO2. The difference lies in how they form. Quartz is a mineral, growing in crystals. Sandstone is a sedimentary rock formed from sand (which is mostly tiny bits of quartz). When sandstone is subjected to high heat and pressure inside the earth, it forms quartzite. The Sioux Quartzite formation is believed to be over 1.5 billion years old, the metamorphic product of a swath of sandstone that blanketed a vast part of what is now North America.
Most of the Sioux quartzite in South Dakota is buried by glacial deposits. A glance at a geologic map of the state shows a fascinating division: the state is bisected, geologically speaking, by the Missouri River. The Sioux quartzite belongs to the East River side of the state, whose surface was shaped by glacial activity that left thousand-foot-deep (305-meter-deep) deposits of silts and clays on top of the underlying hard rock. Geologists believe the exposed Sioux Ridge area was covered with rocks less resistant to erosion than the rocks overlying other portions of the quartzite.
DISCOVERY AND NAME
In 1870, Charles White gave the name "Sioux quartzite" to the outcrops of pink quartzite along the Big Sioux River in northwestern Iowa. The word "Sioux," referring to a group of Native American tribes comprising the Great Sioux Nation, originated in the 18th century as a shortening of the Ojibwa term Nadouessioux. Dakota is another name for Sioux.
The Sioux Quartzite formation lies about 9,800 feet (3,000 meters) thick and 330 miles (535 km) long, forming a sickle shape running eastward from the area around Pierre, South Dakota. Its eastern portion runs into Minnesota, Iowa, and Nebraska. Quartzite is found in many U.S. states from coast to coast, notably in Wisconsin, Idaho, Utah, and Arizona; north of the border in Ontario, Canada, quartzite makes up the Cloche Range of mountains. Significant surface formations of quartzite appear in the United Kingdom.
Apart from its use as a structural stone, quartzite is used as a decorative architectural element on walls, roofs, floors, and stairs. Crushed quartzite is sometimes used in road construction; more finely crushed material is used for poultry grit and abrasive products. Industrial products of quartzite are ferrosilicon (used in steelmaking), industrial sand, silicon metal, and carborundum.
In 2006, four quarries in the southeastern part of South Dakota were still producing quartzite. The main product was aggregate for road construction, with lesser amounts of material sold as rip-rap and railroad ballast. A small amount of dimension stone was also produced.
Many of the oldest and finest buildings of Sioux Falls are made of this handsome stone. Dozens of examples are in the city’s historic district, the Old Courthouse and the Federal Building among them.
Chemical Formula: SiO2
Hardness (Mohs): 7
Specific Gravity: 2.6-2.7
Color: Occurs in an infinite range of colors. Most commonly white, purple, brown, and colorless. Many specimens are multicolored or banded.
|Author: World Trade Press|