The mica group of sheet silicate minerals includes several related materials having nearly perfect basal cleavage. All are monoclinic, with a tendency towards pseudohexagonal crystals, are similar in chemical composition; the nearly perfect cleavage, the most prominent characteristic of mica, is explained by the hexagonal sheet-like arrangement of its atoms. The word mica is derived from the Latin word mica, meaning a crumb, influenced by micare, to glitter. Chemically, micas can be given the general formula X2Y4–6Z8O204,in which X is K, Na, or Ca or less Ba, Rb, or Cs. Structurally, micas can be classed as trioctahedral. If the X ion is K or Na, the mica is a common mica, whereas if the X ion is Ca, the mica is classed as a brittle mica. Muscovite Common micas: Biotite Lepidolite Phlogopite ZinnwalditeBrittle micas: Clintonite Very fine-grained micas, which show more variation in ion and water content, are informally termed "clay micas", they include: Hydro-muscovite with H3O+ along with K in the X site.
Mica is distributed and occurs in igneous and sedimentary regimes. Large crystals of mica used for various applications are mined from granitic pegmatites; until the 19th century, large crystals of mica were quite rare and expensive as a result of the limited supply in Europe. However, their price dropped when large reserves were found and mined in Africa and South America during the early 19th century; the largest documented single crystal of mica was found in Lacey Mine, Canada. Similar-sized crystals were found in Karelia, Russia; the British Geological Survey reported that as of 2005, Koderma district in Jharkhand state in India had the largest deposits of mica in the world. China was the top producer of mica with a third of the global share followed by the US, South Korea and Canada. Large deposits of sheet mica were mined in New England from the 19th century to the 1970s. Large mines existed in Connecticut, New Hampshire, Maine. Scrap and flake mica is produced all over the world. In 2010, the major producers were Russia, United States, South Korea and Canada.
The total global production was 350,000 t. Most sheet mica was produced in Russia. Flake mica comes from several sources: the metamorphic rock called schist as a byproduct of processing feldspar and kaolin resources, from placer deposits, from pegmatites. Sheet mica is less abundant than flake and scrap mica, is recovered from mining scrap and flake mica; the most important sources of sheet mica are pegmatite deposits. Sheet mica prices vary with grade and can range from less than $1 per kilogram for low-quality mica to more than $2,000 per kilogram for the highest quality; the mica group represents 37 phyllosilicate minerals that have a platy texture. The commercially important micas are muscovite and phlogopite, which are used in a variety of applications. Mica's value is based on several of its unique physical properties; the crystalline structure of mica forms layers that can be split or delaminated into thin sheets causing foliation in rocks. These sheets are chemically inert, elastic, hydrophilic, lightweight, reflective, refractive and range in opacity from transparent to opaque.
Mica is stable when exposed to electricity, light and extreme temperatures. It has superior electrical properties as an insulator and as a dielectric, can support an electrostatic field while dissipating minimal energy in the form of heat. Muscovite, the principal mica used by the electrical industry, is used in capacitors that are ideal for high frequency and radio frequency. Phlogopite mica remains stable at higher temperatures and is used in applications in which a combination of high-heat stability and electrical properties is required. Muscovite and phlogopite are used in ground forms; the leading use of dry-ground mica in the US is in the joint compound for filling and finishing seams and blemishes in gypsum wallboard. The mica acts as a filler and extender, provides a smooth consistency, improves the workability of the compound, provides resistance to cracking. In 2008, joint compound accounted for 54% of dry-ground mica consumption. In the paint industry, ground mica is used as a pigment extender that facilitates suspension, reduces chalking, prevents shrinking and shearing of the paint film, increases the resistance of the paint film to water penetration and weathering and brightens the tone of colored pigments.
Mica promotes paint adhesion in aqueous and oleoresinous formulations. Consumption of dry-ground mica in paint, the second-ranked use, accounted for 22% of the dry-ground mica used in 2008. Ground mica is used in the well-drilling industry as an additive to drilling fluids; the coarsely ground mica flakes help prevent the loss of circulation by sealing po
David Haslam Childs FRSA is a British academic and political historian, Professor Emeritus of Politics at the University of Nottingham. His research chiefly concerns the modern German state and the field of German studies, helping the public develop a greater knowledge of the history and politics of the former East and West Germany. Childs was born in Bolton, the son of John Arthur Childs, a police officer, who went on to become Mayor of Bolton, Ellen Childs, he has one sister, who still lives in Bolton. He was educated at Thornleigh Salesian College and the Wigan & District Mining & Technical College in Lancashire, he graduated at the London School of Economics in 1956 before spending a year at the University of Hamburg on a British Council scholarship. He completed his PhD at the University of London in 1962 whilst working part-time as a journalist for Associated Television. Childs' anti-communist views had been developed by works such as Orwell's 1984 and Koestler's Darkness At Noon, as well as his early visits to Germany.
The first was to the communist-organized Festival of Youth And Students in East Berlin. He traveled again to East Berlin just after the rising of June 1953 when the Soviet Army was used to crush the workers' revolt. After completing his PhD, he turned to academic work and was appointed as a lecturer at the University of Nottingham in 1966, he was promoted to Senior Lecturer, reader in 1976. By this time, he was well known for his books on Germany and for his book Marx and the Marxists – An Outline of Practice And Theory. In 1983, Childs was appointed as chairman of the Association for the Study of German Politics and conceived the idea for an Institute of German and Swiss Affairs at the University of Nottingham that focussed on politics and society rather than language and literature, it was established in 1985 with the help of John H. Gunn, a businessman and graduate of the university; the institute's purpose-built centre was opened by then-Prime Minister Margaret Thatcher in 1989, hosting conferences on themes such as the Austrian resistance to National Socialism, ethnic Germans in the Soviet Union.
In 1990, controversy arose as speakers from all of the new East German political parties and the Communist SED argued at a conference in the University's great hall about the future of East Germany. German reunification, in October 1990, coincided with the start of the fall of the institute. John Gunn had presided over the collapse of British & Commonwealth, one of the largest city businesses, could no longer fund the Institute; the slump made it difficult to find alternative supporters. Childs, promoted to professor in 1989, came under great pressure from those who had long disapproved of his line on Germany and Communism, from professional rivals, he was removed from the directorship of the Institute in 1992, took early retirement from the University two years later. He continued to serve as a member of the committee of the British-German Association until 1997. Childs' former students include politicians Neil Carmichael and Kelvin Hopkins, Owain Blackwell, Head of Law at Bolton University.
Childs was one of the few who predicted the collapse of the Berlin Wall and of the East German Republic in 1989, concluding after several visits that it was not sustainable. He made such a prediction at a conference at the University of Dundee in 1981; as Professor Marianne Howarth found in the East German archives, a secret report on this was duly sent back to East Berlin. The Stasi attempted to monitor his activities not only on visits to East Germany but in Britain, his appearance at a conference in Bradford in 1983 was again duly recorded in the Stasi archives. He was put on a Stasi Fahndung list and denounced in DDR publications as a'British imperialist East researcher'. Childs discovered the file that the Stasi had on him which covered a seven-year period; the file revealed that he had, in fact, been spied upon by two British spies, who were two British academics. It revealed that he was regarded by the East German secret police as one of their most serious opponents in Britain. Childs delivered the same'Dundee' analysis at the German Historical Institute in London, 24 November 1987, elsewhere.
He predicted early German reunification and outlined a plan in an interview with Peter Johnson on the West German radio Deutschlandfunk in April 1988, but faced ridicule in reaction. When he spoke at the'Pacific Workshop On German Affairs: The Two Germanies at Forty' about the collapse of the DDR, he again met with strong opposition and ridicule. However, the organiser, Professor Christian Soe, invited him back, after German reunification, in 1991, writing,'We are happy that David Childs, who in April 1989 took a minority position in diagnosing the moribund condition of the East German system, returns to give us a post mortem...' In an article written the day before the opening of the Berlin Wall, published in the Yorkshire Evening Post, 9 November 1989, Childs again predicted full German reunification and welcomed it. The following day The Guardian wrote,'It would mean that a dangerous situation in the heart of Europe has been liquidated...' Childs' wide knowledge of both domestic and international affairs has been utilised by both government and commercial organisations.
He has been a guest speaker on contemporary German themes at in universities across Europe and the United States of America. In 2011, he was invited to talk at the Italian-German Historical Institute, based in Trento, Italy, at a conference on International and multidisciplinary perspectives 20 years after the collapse of communism. Although a long-standing member of the European Movement, a strong supporter of t
Lennox Gardens is a garden square in the Knightsbridge district of London SW1X. It is one of the most exclusive garden squares in Knightsbridge, houses on the square are valued at up to £40 million; the houses surrounding the gardens were built around 1886 as part of the development of Smith's Charity Estate. Nos 1, 3 and 5, 2, 4 and 6, at the northern end of Lennox Gardens on opposite sides of the junction with Walton Street are listed Grade II on the National Heritage List for England as is No 8 opposite the rear of St Columba's Church; the east side of the church faces the entrance to Lennox Gardens from Pont Street. 17–43 Lennox Gardens on the east side and of the gardens and No 52 at the left side of the entrance from Milner Street are listed Grade II. The private communal gardens in the centre of Lennox Gardens are 0.4610 hectares in size. The gardens are laid out on the pitch of the late 19th-century Prince's Club's former Prince's Cricket Ground, which itself had been laid out on Cattleugh's nursery gardens.
John Dunbar and his wife Marianne Faithfull lived in a flat in Lennox Gardens in the late 1960s, as did the American writer Anne Edwards and her husband Leon. James Gilbey, a scion of the Gilbey gin family, owned an apartment in Lennox Gardens and it was here that he would meet Diana, Princess of Wales during their romance from the summer of 1989, their relationship was captured in the Squidgygate tapes. Section 2 of the American poet Charles Wright's 1983 poem A Journal of English Days is set during a rainy afternoon in Lennox Gardens where the narrator imagines the Greek ferryman of the underworld, Charon crossing the River Thames in the rain. Section 4 of the poem depicts a walk around the area surrounding Lennox Gardens. Lord Wakehurst and his family lived in a house in Lennox Gardens in the 1950s, his son, the future businessman and art collector Robert Loder let his friend Jonathan Gathorne-Hardy stay in a flat on the top floor of their property. Gathorne-Hardy recalled living in Lennox Gardens in Half an Arch.
George Devey's design for a house for Samuel Juler Wyand at 25 Lennox Gardens is in the collection of the British Architectural Library. The average price of a property in Lennox Gardens was £2.2 million in 2018