| Chaoite | |
|---|---|
| General | |
| Category | Native element mineral |
| Formula | C |
| IMA symbol | Ch[1] |
| Strunz classification | 1.CB.05b |
| Crystal system | Hexagonal |
| Crystal class | Dihexagonal dipyramidal (6/mmm) H-M symbol: (6/m 2/m 2/m) |
| Space group | P6/mmm |
| Unit cell | a = 8.948 Å, c = 14.078 Å; Z = 168 |
| Identification | |
| Colour | Black |
| Crystal habit | Thin 3-15 μm intergrowth lamallae with graphite |
| Mohs scale hardness | 1 - 2 |
| Lustre | Submetallic |
| Diaphaneity | Opaque |
| Specific gravity | 3.43 (calculated) |
| References | [2][3][4] |
Chaoite, orwhite carbon, is amineral described as anallotrope ofcarbon whose existence is disputed. It was discovered in shock-fused graphitegneiss from theRies crater in Bavaria. It has been described as slightly harder than graphite, with a reflection colour of grey to white.[5] From itselectron diffraction pattern, the mineral has been considered to have acarbyne structure,[6] thelinear 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 termedceraphite.[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 ofpolywater".[9]
Chaoite was first described fromMöttingen,Ries Crater,Nördlingen,Bavaria, Germany and approved by theIMA in 1969.[3] The mineral was named for USGS petrologistEdward C. T. Chao (1919-2008).[3] At thetype locality in Bavaria chaoite occurs in graphite bearinggneiss that has undergoneshock metamorphism.[2] It has also been reported from meteorites including the Goalpara meteorite inAssam, the Dyalpur meteorite inUttar Pradesh inIndia and thePopigai impact structure in theAnabarskii massif of EasternSiberia.[2][3] Minerals associated with chaoite include: graphite,zircon,rutile,pseudobrookite,magnetite, nickeliferouspyrrhotite andbaddeleyite.[2]
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, PrintISBN 978-1-57444-512-1 eBookISBN 978-1-4200-2758-7Contents link