Mathematics – Logic
Scientific paper
Oct 1965
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1965gecoa..29.1131e&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 29, Issue 10, pp.1131-1136
Mathematics
Logic
16
Scientific paper
Detailed studies of more than fifty nodules from fifteen iron meteorites were performed in reflected light and with the microprobe. They were taken from the meteorites Bethany, Braunau, Canon Diablo, Cape York, Charcas, Corizatillo, Dalgaranga, Delegate. Hoba West, N'Goureyma, Obernkirchen, Odessa, Russel Gulch,Toluca (Xiquipilco) and Trenton. According to the mineralogical composition the following different groups of nodules wore identified: 1. (1) Graphite nodules with traces of sulphides. 2. (2) Graphite-troilite nodules. 3. (3) Troilito nodules devoid of graphite. Graphite nodules are comparatively rare, and composed mainly of graphite together with schreibersite, cohenite and traces of sphalerite. The majority of graphite occurs as idiomorphic or compact cliftonite crystals. No genetical relationship have been found to exist between cliftonite and diamond on the one hand, and cliftonite and iron carbides in the other. A graphite nodule from Cañon Diablo contains besides cliftonite another younger feathery graphite generation. Graphite-troilite nodules are very complicated both in mineralogical composition and textures. In this group the following graphite generations were observed: 1. (a) cliftonite, 2. (b) crescentic graphite similar to "retorte graphite", 3. (c) separate grains preferably oriented // (0001) of troilite, 4. (d) palmetten graphite, 5. (e) small graphite spherulites, 6. (f) big spherules with troilito nuclii. Nodules of this group contain also: troilite, daubreolite, a new mineral (Fe, Mg, Mn) x Cr y S z , iron alabandite, sphalerite (paramorph after wurtzite), native copper, chalcopyrrhotite, mackinawite, rutile, olivine, clinoenstatite, plagioclase (maskelynite?) and terrestrial pentlandite, chalcopyrite, a new Cu-Cr-sulphide, magnetite and maghemite. The origin of diamond in Cañon Diablo iron is also discussed in detail. The third group is the most abundant among all nodules. They consist mainly of troilite and daubreelite. Monomineralic nodules are not rare. Other minerals present are: chromsphinol, native copper, chalcopyrrhotite, sphalerite, a new mineral CrS, and secondary pentlandite, and chalcopyrite. This group is in general devoid of silicates. The meteorites Bethany, Braunau and N'Goureyma suffered cosmic heating causing certain changes in the mineralogical composition of their nodules. Mechanical deformation and recrystallization textures due to cosmic collisions and meteorite impacts are described in detail.
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