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Chaoit vom Ries : Literatur dazu ?

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giantcrystal:
Hallo aus Mittelfranken

Ich habe hier gerade ein Stück Chaoit (?) vom Ries vorliegen, Typlokalität Möttingen : ausgesprochen unscheinbare schwarze Krusten.

Überraschenderweise finde ich hierzu kaum Literatur und Infos im Netz, obwohl die Entdeckung einer neuen Kohlenstoffmodifikation doch normalerweise Grund genug dazu wäre.

Selbst die Eingabe des Originalzitates El Goresy, A. & Donnay, G. (1968) : A new allotriomorphic form of carbon from the Ries Crater
bringt nur zwei kümmerliche Resultate.

Mache ich etwas falsch....oder hat jemand mehr Infos ?  Und gibt es das Mineral überhaupt ...laut den spärlichen Infos soll es sich um dünne Schichten zwischen Graphitlamellen handeln...

Danke für die Hilfe

Thomas
 

stollentroll:
Hallo Thomas,
schwarze Krusten sind garantiert kein Chaoit.

Ich habe für Joe Mandarinos geplante (und nach seinem Tod sehr verzögerte) Encyclopedia of Minerals den Beitrag über Chaoit verfasst. Ich geb hier mal die wesentlichen Auszüge daraus:

CRYSTALLOGRAPHY: hexagonal, space group P6/mmm (?).
   Unit cell data: a 8.948, c 14.078 Å, V 976.16 Å3, Z 168 (?) for natural material (El Goresy and Donnay, 1968), a 8.940, c 14.097 Å for synthetic material (Li et al., 2007, from micro-area X-ray diffraction and HRTEM).
   Class 6/mmm, c:a = 1.573:1.
   Morphology: No separate forms observed, sometimes tabular on (001).
   Twinning:  not mentioned.
   Crystal structure: not determined. Chaoite is regarded as a carbyne. Two forms of carbyne chains are known, α-carbyne (polyyne, with alternating single and triple bonds), and β-carbyne (polycumulene, only with double bonds) with a distance between two neighboring carbon atoms of 1.374 and 1.337 Å. In carbyne crystals, the chains are arranged in an hexagonal array parallel to c. Calculations by molecular mechanics (Belenkov and Mavrinky, 2008) for a hypothetical ideal carbyne crystal with only Van der Waals forces between the chains yielded a subcell P3m1, a 3.553, c 1.337 Å, Z 1. Obtained synthetic and natural material cannot be considered as a pure linear carbon modification (with only sp1 hybridization of electron orbitals) because of cross-linking between the chains (with linking carbon atoms in sp2 hybridized state as in graphite and fullerene or sp3 as in diamond), distortion of the chains or impurity atoms. The degree of cross-linking gives rise to a wide variation in physical properties (Li et al., 2007) and affect the distances of the carbyne chains. According to Chuan et al. (2003), chaoite might be stabilized by the intercalation of Si or Fe, located in galleries between layers of carbyne, where straight or kinked carbon chains were held together by Van der Waals forces.
   X-ray powder diffraction data: 4.47 (very very strong) (110), 4.26 (very very strong) (111), 4.12 (very strong) (103, impurity ?), 3.03 (strong) (203), 2.55 (strong) (301), 2.28 (strong) (205).
GENERAL APPEARANCE: Thin lamellae, alternating with graphite, small particles, flakes tabular on (001) up to 50 µm in size.
PHYSICAL PROPERTIES:
   Metallic; opaque; megascopic color unknown or black, streak not given.
   Hardness weak, slightly harder than graphite; tenacity not given.
   Cleavage and fracture not given.
   Density: 3.43 g/cm3 (calc.). The calculated density of 1.36 g/cm3 for an ideal carbyne crystal from the data of Belenkov and Mavrinky (2008) indicate either a high deviation from the ideal carbyne crystal structure or questionable Z and/or unit cell data for chaoite.
OPTICAL PROPERTIES: In reflected light: grey to white, no anisotropism observed (probably due to the extremely small grain size), much more strongly reflecting than graphite.
CHEMICAL ANALYTICAL DATA: Electron-microprobe analysis gave carbon as the only major element detected, and traces of Si and Cl (due to contamination by the glass matrix and mounting material) (El Goresy & Donnay, 1968). Electron microprobe analysis (EDX) C > 90, Si 0.8 - 2.0, Fe 0.3, O 7 % (Chuan et al., 2003). The ideal formula requires: C total 100.00 wt.%.
LOCALITIES: Möttingen, Ries Crater, Bavaria, Germany (El Goresy and Donnay, 1968; El Goresy 1969). Ca-poor achondrite (ureilite) meteorites Novo Urei, Karamsinka, Russia (Vdovykin 1969) and Haverö, Finland (Vdovykin 1972). Murchison carbonaceous chondrite meteorite, Victoria, Australia (Gilkes et al. 1992). Diamond mine, Liao-Ning province, northeastern China (Chuan et al., 2003).
OCCURRENCE: From the Ries Crater in shock-fused graphite gneisses, as thin lamellae (3 - 15 µm wide) alternating with graphite and perpendicular to the (001) face of graphite. Together with graphite, rutile, pseudobrookite, magnetite, pyrrhotite, and baddeleyite. From the Novo Urei meteorite in small diamond-graphite particles, together with chromite and kamacite. From the Murchison meteorite in small particles, typically 10 nm in size. In small black flakes, 5 - 50 µm in size from the Liao-Ning diamond mine.
In synthesis experiments, crystalline α- and β-carbyne were obtained by step-like shock-wave compression from graphite (peak pressure 36 GPa, maximum temperature 730 K). It is assumed that carbyne may be formed via single bond opening in the graphite basal plane (Milyavskiy et al., 2002).
RELATIONSHIP TO OTHER SPECIES: Polymorphous (allotropic) with graphite, diamond, lonsdaleite, and fullerene. Chaoite is regarded as a carbyne.
NAME: For Edward Ching-te Chao (1919 - 2008), Petrologist, U.S. Geological Survey, for his work on the mineralogy and shock phenomena of the Ries Crater.
COMMENTS: IMA approved (1968-012). As unnamed mineral described by El Goresy and Donnay (1968), as chaoite without new data by El Goresy (1969). The existence of carbyne was doubted and the powder diffraction data assumed to represent a mixture of quartz and nontronite (Smith and Buseck 1982). Additional natural occurrences and synthesis of pure carbon material (Li et al., 2007) with X-ray diffraction pattern very close to the data of El Goresy and Donnay (1968) and several other synthesis experiments established the existence of carbyne (with a certain degree of cross-linking between carbyne chains).
REFERENCES:
Belenkov, E.A. and Mavrinsky, V.V. (2008) Crystal structure of a perfect carbyne. Crystallography Reports 53, 83-87
Chuan, X.-Y., Zheng, Z. and Chen, J. (2003) Flakes of natural carbyne in a diamond mine. Carbon 41, 1877-1880
El Goresy, A. (1969) Eine neue Kohlenstoff-Modifikation aus dem Nördlinger Ries. Naturwissenschaften 56, 493-494.
El Goresy, A. and Donnay, G. (1968) A new allotropic form of carbon from the Ries Crater. Science 161, 363-364.
Gilkes, K.W.R., Gaskell, P.H., Russell, S.S., Arden, J.W. and Pillinger, C.T. (1992) Do carbynes exist as interstellar material after all ? Meteoritics 27, 224
Li, S., Ji, G., Huang, Z., Zhang, F. and Du, Y. (2007) Synthesis of chaoite-like macrotubes at low temperature and ambient pressure. Carbon 45, 2946-2950
Milyavskiy, V.V., Zhuk, A.Z. and Khishchenko, K.V. (2002) Novel Carbon Materials: Possibility of Shock-Wave Synthesis.- Defect and Diffusion Forum 208/209, 161-174
Smith, P.P.K. and Buseck, P.R. (1982) Carbyne forms of carbon: do they exist ? Science 216, 984-986
Vdovykin, G.P. (1969) Novaya geksagonal’naya modifikatsiya ugleroda v meteoritakh. Geokhimia, No. 9, 1145-1148.
Vdovykin, G.P. (1972) Forms of carbon in the new Haverö ureilite of Finland. Meteoritics 7, 547-552.
CONTRIBUTOR: Thomas Witzke, Germany.

raritätenjäger:
Hallo,

nun habe auch ich so ein Stück herumzuliegen. In der Beschreibung zum damaligen Kauf stand, dass es sich bei dem Chaoit um Bestandteile in glasig aufgeschmolzenen Glaspartien ("Flädle") im Suevitgestein handeln solle. Das scheint ja nun nicht korrekt zu sein. Es befinden sich auch kleine Flächen aus staubförmigem schwarzem Material auf der Stufe. Ist das dann wenigstens der Chaoit oder siegt hier mal wieder die Erkenntnis, dass du in diesem Lande beim Kauf seltener Systematik jedes zweite Mal ins WC greifst...?

Gruß
Andreas

giantcrystal:
Zu ergänzen bleibt noch, das nach verschiedenen Quellen Chaoit auch als "White carbon" bezeichnet wird. Wie verträgt sich das mit der offiziellen Farbangabe "Schwarz" ?

Glück Auf

ein etwas verwirrter Thomas

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