Ball clays are kaolinitic

Kaolinite

Kaolinite is a clay mineral, part of the group of industrial minerals, with the chemical composition Al2Si2O54. It is a layered silicate mineral, with one tetrahedral sheet linked through oxygen atoms to one octahedral sheet of alumina octahedra...

 sedimentary clay

Clay

Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...

s, that commonly consist of 20-80% kaolinite

Kaolinite

Kaolinite is a clay mineral, part of the group of industrial minerals, with the chemical composition Al2Si2O54. It is a layered silicate mineral, with one tetrahedral sheet linked through oxygen atoms to one octahedral sheet of alumina octahedra...

, 10-25% mica

Mica

The mica group of sheet silicate minerals includes several closely related materials having highly perfect basal cleavage. All are monoclinic, with a tendency towards pseudohexagonal crystals, and are similar in chemical composition...

, 6-65% quartz

Quartz

Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...

. Localized seams in the same deposit have variations in composition, including the quantity of the major mineral

Mineral

A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...

s, accessory minerals and carbonaceous

Carbonaceous

Carbonaceous is the defining attribute of a substance rich in carbon. Particularly, carbonaceous hydrocarbons are very unsaturated, high-molecular-weight hydrocarbons, having an elevated carbon:hydrogen ratio....

 materials such as lignite

Lignite

Lignite, often referred to as brown coal, or Rosebud coal by Northern Pacific Railroad,is a soft brown fuel with characteristics that put it somewhere between coal and peat...

. They are fine-grained and plastic in nature.

Ball clays are relatively scarce deposits due to the combination of geological factors needed for their formation and preservation. They are mine

Mining

Mining is the extraction of valuable minerals or other geological materials from the earth, from an ore body, vein or seam. The term also includes the removal of soil. Materials recovered by mining include base metals, precious metals, iron, uranium, coal, diamonds, limestone, oil shale, rock...

d in parts of the Eastern United States and from three sites in Devon

Devon

Devon is a large county in southwestern England. The county is sometimes referred to as Devonshire, although the term is rarely used inside the county itself as the county has never been officially "shired", it often indicates a traditional or historical context.The county shares borders with...

 and Dorset

Dorset

Dorset , is a county in South West England on the English Channel coast. The county town is Dorchester which is situated in the south. The Hampshire towns of Bournemouth and Christchurch joined the county with the reorganisation of local government in 1974...

 in South West England

England

England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...

. They are commonly used in the construction of many ceramic articles, where their primary role is to either to impart plasticity or to aid rheological stability during the shaping processes.

History

The name "ball clay" is believed to derive from the time when the clay was mined by hand. It was cut into 15 to 17-kilogram cubes and during transport the corners of the cubes became rounded off leaving "balls".

The ceramic

Ceramic

A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...

 use of ball clays in Britain

Great Britain

Great Britain or Britain is an island situated to the northwest of Continental Europe. It is the ninth largest island in the world, and the largest European island, as well as the largest of the British Isles...

 dates back to at least the Roman

Roman Empire

The Roman Empire was the post-Republican period of the ancient Roman civilization, characterised by an autocratic form of government and large territorial holdings in Europe and around the Mediterranean....

 era. More recent trade began when a clay was needed to construct tobacco pipes in the 16th and 17th century. In 1771 Josiah Wedgwood

Josiah Wedgwood

Josiah Wedgwood was an English potter, founder of the Wedgwood company, credited with the industrialization of the manufacture of pottery. A prominent abolitionist, Wedgwood is remembered for his "Am I Not A Man And A Brother?" anti-slavery medallion. He was a member of the Darwin–Wedgwood family...

 signed a contract for 1400 tons a year of ball clay with Thomas Hyde of Purbeck, enabling him to fire thinner walled ceramics.

See also

• Ball clay and the Stover Canal
• Purbeck Ball Clay
  Purbeck Ball Clay
  Purbeck Ball Clay is a concentration of ball clay found on the Isle of Purbeck in the English county of Dorset.-Geology:The main concentration of ball clay in Dorset is to the north of the Purbeck Hills centred around Norden. Ball clays are sedimentary in origin...