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Chaoite

Chaoite, or white carbon, is a mineral described as an allotropeofcarbon whose existence is disputed. It was discovered in shock-fused graphite gneiss from the Ries crater in Bavaria. It has been described as slightly harder than graphite, with a reflection colour of grey to white.^[5] From its electron diffraction pattern, the mineral has been considered to have a carbyne structure,^[6] the linear acetylenic carbon allotrope of carbon. A later report has called this identification, and the very existence of carbyne phases, into question, arguing that the new reflections in the diffraction pattern are due to clay impurities.^[7]

It has been claimed that an identical form can be prepared from graphite by sublimation at 2700-3000 K or by irradiating it with a laser in high vacuum. This substance has been termed ceraphite.^[8]

A review cautions that "in spite of these seemingly definitive reports … several other groups have tried unsuccessfully to reproduce these experiments. Independent confirmatory work is obviously needed … and at the present time white graphite appears to be the carbon analog of polywater".^[9]

Chaoite was first described from Möttingen, Ries Crater, Nördlingen, Bavaria, Germany and approved by the IMA in 1969.^[3] The mineral was named for USGS petrologist Edward C. T. Chao (1919-2008).^[3] At the type locality in Bavaria chaoite occurs in graphite bearing gneiss that has undergone shock metamorphism.^[2] It has also been reported from meteorites including the Goalpara meteorite in Assam, the Dyalpur meteorite in Uttar PradeshinIndia and the Popigai impact structure in the Anabarskii massif of Eastern Siberia.^[2][3] Minerals associated with chaoite include: graphite, zircon, rutile, pseudobrookite, magnetite, nickeliferous pyrrhotite and baddeleyite.^[2]

• Glossary of meteoritics

Frans J. M. Rietmeijer and Alessandra Rotundi, Chapter 16. Natural Carbynes, Including Chaoite, on Earth, in Meteorites, Comets, Circumstellar and Interstellar Dust, in Polyynes: Synthesis, Properties, and Applications, Edited by Franco Cataldo, CRC Press 2005, Pages 339–370, Print ISBN 978-1-57444-512-1 eBook ISBN 978-1-4200-2758-7 Contents link