Ball clays are kaolinitic

sedimentary Sedimentary rocks are types of rock (geology), rock that are formed by the accumulation or deposition of mineral or organic matter, organic particles at Earth#Surface, Earth's surface, followed by cementation (geology), cementation. Sedimentati ...

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay par ...

s that commonly consist of 20–80% kaolinite, 10–25%

mica Micas ( ) are a group of silicate minerals whose outstanding physical characteristic is that individual mica crystals can easily be split into extremely thin elastic plates. This characteristic is described as perfect basal cleavage. Mica is ...

, 6–65%

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical form ...

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

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. ( ...

s, accessory minerals and

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...

aceous materials such as

lignite Lignite, often referred to as brown coal, is a soft, brown, combustible, sedimentary rock formed from naturally compressed peat. It has a carbon content around 25–35%, and is considered the lowest rank of coal due to its relatively low heat ...

. They are fine-grained and plastic in nature, and, unlike most

earthenware Earthenware is glazed or unglazed nonvitreous pottery that has normally been fired below . Basic earthenware, often called terracotta, absorbs liquids such as water. However, earthenware can be made impervious to liquids by coating it with a ce ...

clays, produce a fine quality white-coloured

pottery Pottery is the process and the products of forming vessels and other objects with clay and other ceramic materials, which are fired at high temperatures to give them a hard and durable form. Major types include earthenware, stoneware and por ...

body when fired, which is the key to their popularity with potters. Ball clays are relatively scarce deposits due to the combination of geological factors needed for their formation and preservation. They are

mine Mine, mines, miners or mining may refer to: Extraction or digging * Miner, a person engaged in mining or digging *Mining, extraction of mineral resources from the ground through a mine Grammar *Mine, a first-person English possessive pronoun ...

d in parts of the Eastern United States and from three sitesThe

Bovey Basin The Bovey Formation is a deposit of sands, clays and lignite, probably over 1000 feet thick. It lies in a sedimentary basin termed the Bovey Basin which extends from Bovey Tracey to Newton Abbot in South Devon, England. The Bovey Basin lies ...

in South Devon, the Petrockstowe Basin in North Devon and the Wareham Basin in South Dorset. in

Devon Devon ( , historically known as Devonshire , ) is a ceremonial and non-metropolitan county in South West England. The most populous settlement in Devon is the city of Plymouth, followed by Devon's county town, the city of Exeter. Devon is ...

and

Dorset Dorset ( ; archaically: Dorsetshire , ) is a county in South West England on the English Channel coast. The ceremonial county comprises the unitary authority areas of Bournemouth, Christchurch and Poole and Dorset (unitary authority), Dors ...

in South West

England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...

. They are commonly used in the construction of many ceramic articles, where their primary role, apart from their white colour, is either to impart plasticity or to aid

rheological Rheology (; ) is the study of the flow of matter, primarily in a fluid (liquid or gas) state, but also as "soft solids" or solids under conditions in which they respond with plastic flow rather than deforming elastically in response to an appli ...

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 A ceramic is any of the various hard, brittle, heat-resistant and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcelain ...

use of ball clays in

Britain Britain most often refers to: * The United Kingdom, a sovereign state in Europe comprising the island of Great Britain, the north-eastern part of the island of Ireland and many smaller islands * Great Britain, the largest island in the United King ...

dates back to at least the

Roman Roman or Romans most often refers to: *Rome, the capital city of Italy *Ancient Rome, Roman civilization from 8th century BC to 5th century AD *Roman people, the people of ancient Rome *''Epistle to the Romans'', shortened to ''Romans'', a letter ...

era. More recent trade began when a clay was needed to construct

tobacco pipes A tobacco pipe, often called simply a pipe, is a device specifically made to smoke tobacco. It comprises a chamber (the bowl) for the tobacco from which a thin hollow stem (shank) emerges, ending in a mouthpiece. Pipes can range from very sim ...

in the 16th and 17th century. In 1771

Josiah Wedgwood Josiah Wedgwood (12 July 1730 – 3 January 1795) was an English potter, entrepreneur and abolitionist. Founding the Wedgwood company in 1759, he developed improved pottery bodies by systematic experimentation, and was the leader in the indust ...

signed a contract for 1400 tons a year of ball clay with Thomas Hyde of Purbeck,See

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 on Norden. Ball clays are sedimenta ...

enabling him to fire thinner-walled ceramics.

Notes

References

{{Pottery Pottery Geology of Devon Clay Industrial minerals

History

See also

Notes

References