China Clay Sculpture Wheal Martyn Museum,St Austell - geograph

China stone is a medium grained,

feldspar Feldspars are a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagioclase'' (sodium-calcium) felds ...

-rich partially kaolinised

granite Granite () is a coarse-grained ( phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies un ...

characterized by the absence of

iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in ...

-bearing minerals.Cornwall County Council website, ''China clay and china stone''
undated, URL retrieved on 14 September 2007 It is mainly used for making

porcelain Porcelain () is a ceramic material made by heating substances, generally including materials such as kaolinite, in a kiln to temperatures between . The strength and translucence of porcelain, relative to other types of pottery, arises main ...

, hence the name, and coatings for paper. Its discovery in the mid-18th century was a crucial event in the development of the English porcelain industry. The

Quaker Quakers are people who belong to a historically Protestant Christian set of denominations known formally as the Religious Society of Friends. Members of these movements ("theFriends") are generally united by a belief in each human's abili ...

William Cookworthy William Cookworthy (12 April 170517 October 1780) was an English Quaker minister, a successful pharmacist and an innovator in several fields of technology. He was the first person in Britain to discover how to make hard-paste porcelain, like t ...

(1705-1780) was probably the first to realize its significance, around 1745, though his attempts at commercial exploitation, culminating in the founding of Plymouth porcelain in 1768, did not achieve long-term success. A letter of a Dr Richard Pococke from 1750 reports being shown near

Lizard Point, Cornwall Lizard Point () in Cornwall is at the southern tip of the Lizard Peninsula. It is situated half-a-mile (800 m) south of Lizard village in the civil parish of Landewednack and about 11 miles (18 km) southeast of Helston. Lizard Poi ...

, a deposit "mostly valued for making porcelane ... and they get five pounds a ton for the manufacture of porcelane now carrying on at Bristol" (this Bristol enterprise being Lund's Bristol ware). However, this Lizard material was probably

soapstone Soapstone (also known as steatite or soaprock) is a talc-schist, which is a type of metamorphic rock. It is composed largely of the magnesium rich mineral talc. It is produced by dynamothermal metamorphism and metasomatism, which occur in the ...

(steatite), which was very useful in reducing the tendency of

soft-paste porcelain Soft-paste porcelain (sometimes simply "soft paste", or "artificial porcelain") is a type of ceramic material in pottery, usually accepted as a type of porcelain. It is weaker than "true" hard-paste porcelain, and does not require either the hig ...

to shatter with rapid changes in temperature. Existing English

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 ...

companies, mostly from

Staffordshire Staffordshire (; postal abbreviation Staffs.) is a landlocked county in the West Midlands region of England. It borders Cheshire to the northwest, Derbyshire and Leicestershire to the east, Warwickshire to the southeast, the West Midlands C ...

, swiftly moved to exploit the deposits. For the first time English companies, led by Plymouth, were able make "true"

hard-paste porcelain Hard-paste porcelain, sometimes "true porcelain", is a ceramic material that was originally made from a compound of the feldspathic rock petuntse and kaolin fired at very high temperature, usually around 1400 °C. It was first made in China ...

, rather than

, although the industry had already been experimenting with bone ash, and china stone soon became used in the highly successful English

bone china Bone china is a type of ceramic that is composed of bone ash, feldspathic material, and kaolin. It has been defined as "ware with a translucent body" containing a minimum of 30% of phosphate derived from animal bone and calculated calcium phos ...

instead. Its mineral content includes

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 f ...

, feldspar and

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 ...

; accessory minerals include

kaolinite Kaolinite ( ) is a clay mineral, with the chemical composition Al2 Si2 O5( OH)4. It is an important industrial mineral. It is a layered silicate mineral, with one tetrahedral sheet of silica () linked through oxygen atoms to one octahed ...

and

fluorspar Fluorite (also called fluorspar) is the mineral form of calcium fluoride, CaF2. It belongs to the halide minerals. It crystallizes in isometric cubic habit, although octahedral and more complex isometric forms are not uncommon. The Mohs sca ...

. It is found in one area of

Cornwall Cornwall (; kw, Kernow ) is a Historic counties of England, historic county and Ceremonial counties of England, ceremonial county in South West England. It is recognised as one of the Celtic nations, and is the homeland of the Cornish people ...

in the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and ...

, near

St Austell St Austell (; kw, Sans Austel) is a town in Cornwall, England, south of Bodmin and west of the border with Devon. St Austell is one of the largest towns in Cornwall; at the 2011 census it had a population of 19,958. History St Austell ...

, and is the UK’s only indigenous source of feldspathic material commercially extracted. Production in the four years up to 2003 averaged 2,800

tonnes The tonne ( or ; symbol: t) is a unit of mass equal to 1000 kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton to distinguish it from the non-metric units of the short ton (United States c ...

per year. Other names include Cornish or Cornwall stone. undated, URL retrieved on 14 September 2007 It is sometimes confused with

petuntse Petuntse (from 白墩子 in pinyin: ), also spelled petunse and ''bai dunzi'', ''baidunzi'', is a historic term for a wide range of micaceous or feldspathic rocks. However, all will have been subject to geological decomposition processes that res ...

or "porcelain stone", which, although somewhat similar, is a different rock. For most of the 20th century production was dominated by

English China Clays English China Clays PLC, or ECC, was a mining company involved in the extraction of china clay, based in St Austell, Cornwall. It was once a constituent of the FTSE 100 Index but in 1999 was acquired by Imetal. History English China Clays was i ...

Ltd/Plc, once a constituent of the

FTSE 100 Index The Financial Times Stock Exchange 100 Index, also called the FTSE 100 Index, FTSE 100, FTSE, or, informally, the "Footsie" , is a share index of the 100 companies listed on the London Stock Exchange with (in principle) the highest marke ...

, but in 1999 acquired by the French company now called

Imerys Imerys S.A. is a French multinational company which specialises in the production and processing of industrial minerals. It is headquartered in Paris and is a constituent of the CAC Mid 60 index. Imerys has operations in over 40 countries and ...

. The

St Austell and Clay Country Eco-town The St Austell and Clay Country Eco-town is a plan to build a new town on a cluster of sites owned by mining company Imerys near St Austell, in Cornwall, UK. The plan was given outline government approval in July 2009. The plan would need to gain ...

is a plan to build a new town on a cluster of sites owned by Imerys near

. The plan was given outline government approval in July 2009. The plan would need to gain full planning permission before construction commenced.

Notes

References

*Honey, W.B., ''Old English Porcelain: A Handbook for Collectors'', 1977, 3rd edn. revised by Franklin A. Barrett, Faber and Faber, *Elkington, John
"Reclaiming the Cornish Moonscape"
''

New Scientist ''New Scientist'' is a magazine covering all aspects of science and technology. Based in London, it publishes weekly English-language editions in the United Kingdom, the United States and Australia. An editorially separate organisation publish ...

'', 5 Jan 1978, page 14 *Spero, Simon, Battie, David, ed., ''Sotheby's Concise Encyclopedia of Porcelain'', 1990, Conran Octopus. Igneous rocks Geology of Cornwall English pottery {{petrology-stub

See also

Notes

References