DOCSLIB.ORG

WASHINGTON COUNTY IRON METEORITE RECLASSIFIED AS IIIAB Dwijesh Ray and S

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
WASHINGTON COUNTY IRON METEORITE RECLASSIFIED AS IIIAB Dwijesh Ray and S 77th Annual Meteoritical Society Meeting (2014) 5159.pdf WASHINGTON COUNTY IRON METEORITE RECLASSIFIED AS IIIAB Dwijesh Ray and S. Ghosh. PLANEX, Physical Research Labor- atory, Ahmedabad 380009, India. E-mail: [email protected]. Introduction: Washington County (WC) was classified as ‘Ataxite’ [1]. Previous metallographic study including the α2- zone of the fusion crust, bulk composition and noble gas revealed WC as chemically ungrouped ataxite with traces of volume cor- related solar noble gases [2, 3]. In an effort to search for the poss- ible carrier phase of solar noble gases, the present study has led to a reappraisal of texture, phase composition and bulk composi- tion of WC, leading to its reclassification. Results: WC iron shows a finely recrystallised matrix (mean size: 30 μm) of granular kamacite (mean Ni: 7.25 ± 0.07 wt%). Evenly dispersed particles (5-20 μm) of high-Ni taenite (Ni: 32.3 ± 1.12 wt%), Ni-rich schreibersite (Ni: 46.6 ± 0.08 wt%) and sporadically distributed angular to subangular particles of high carbon phase (HCP) of variable composition (C: 74- 15 wt%; Ni: 1.2-6.5 wt%) are common in the kamacite. Signatures of anneal- ing are clearly evident from coarsening of kamacite grains (mean size: 70 μm), spheroidisation of taenite and schreibersite par- ticles, development of cavernous (kamacite-filled pits) low-Ni taenite phase (Ni: 22 wt%) and a high degree of decomposition of cohenite to HCP. Bulk chemical data of WC (Co: 0.56 wt%, Cr: 0.01 wt%, Ga: 18 ppm, Ge: 33 ppm, Ir: 0.01 ppm and Cu: 220 ppm) closely correspond to the available data [2, 4]. Discussion: Strong effect of secondary reheating essentially due to high degree of shock (>750 kb) has been identified for complete destruction of all primary textures and formation of the thoroughly recrystallised granulated kamacite matrix decorated with evenly distributed particles of taenite and schreibersite. Based on the abundance of metals and non- metals, their parage- nesis and of course, phase compositions authors assign WC the structural group ‘Reheated Medium Octahedrite’. Shock altera- tion to the extent of kamacite recrystallisation coupled with low Hv ~ 150 ± 5 [2] confirms its well-annealed status. The second- ary annealing is natural and not artificial, is indicated from ho- mogeneous equilibrium texture in the interior core and presence of zonal macrostructure that shows progressively decreasing de- gree of reheating from outer margin to interior core [5]. By con- trast, artificially heated texture mostly as patchy zones of dise- quilibrium melting like Santa Rosa [2] is absent in WC. WC falls within well defined fractionated group IIIAB, more specifically IIIB despite a strong reheating [6, 7]. This chemical grouping reaffirms that the earlier ataxite status for WC needs a revision because ataxites largely belong to chemical group IVB with bulk Ni content of 16 to 30 wt%. Estimated metallographic cooling rate of WC is 100oC/Ma based on its bulk Ni content [8]. HCP could be a possible carrier phase for solar noble gases? Fur- ther studies are in progress. Acknowledgement: We thank Carl Francis for the WC sample. References: [1] Palache C. and Shannon E.V. 1928. Am. Min. 13:406-409. [2] Buchwald V.F. 1975. Handbook of Iron Met. 1426pp. [3] Murty S.V.S. and Ranjith P.M. 2014. LPSC 45, #1110. [4] Wasson J.T. and Schaudy R. 1971. Icarus 14:59-70. [5] Cech R.E. 1962. GCA 26: 993-998. [6] Scott E.R.D. 1979. Min Mag 43:415-421. [7] Yang J. and Goldstein J.I. 2005. MAPS 40:239-253. [8] Yang J. and Goldstein J.I. 2005. GCA 70:3197- 3215. .
Load more

Recommended publications
  • Handbook of Iron Meteorites, Volume 3
    Sierra Blanca - Sierra Gorda 1119 ing that created an incipient recrystallization and a few COLLECTIONS other anomalous features in Sierra Blanca. Washington (17 .3 kg), Ferry Building, San Francisco (about 7 kg), Chicago (550 g), New York (315 g), Ann Arbor (165 g). The original mass evidently weighed at least Sierra Gorda, Antofagasta, Chile 26 kg. 22°54's, 69°21 'w Hexahedrite, H. Single crystal larger than 14 em. Decorated Neu­ DESCRIPTION mann bands. HV 205± 15. According to Roy S. Clarke (personal communication) Group IIA . 5.48% Ni, 0.5 3% Co, 0.23% P, 61 ppm Ga, 170 ppm Ge, the main mass now weighs 16.3 kg and measures 22 x 15 x 43 ppm Ir. 13 em. A large end piece of 7 kg and several slices have been removed, leaving a cut surface of 17 x 10 em. The mass has HISTORY a relatively smooth domed surface (22 x 15 em) overlying a A mass was found at the coordinates given above, on concave surface with irregular depressions, from a few em the railway between Calama and Antofagasta, close to to 8 em in length. There is a series of what appears to be Sierra Gorda, the location of a silver mine (E.P. Henderson chisel marks around the center of the domed surface over 1939; as quoted by Hey 1966: 448). Henderson (1941a) an area of 6 x 7 em. Other small areas on the edges of the gave slightly different coordinates and an analysis; but since specimen could also be the result of hammering; but the he assumed Sierra Gorda to be just another of the North damage is only superficial, and artificial reheating has not Chilean hexahedrites, no further description was given.
    [Show full text]
  • Handbook of Iron Meteorites, Volume 2 (Canyon Diablo, Part 2)
    Canyon Diablo 395 The primary structure is as before. However, the kamacite has been briefly reheated above 600° C and has recrystallized throughout the sample. The new grains are unequilibrated, serrated and have hardnesses of 145-210. The previous Neumann bands are still plainly visible , and so are the old subboundaries because the original precipitates delineate their locations. The schreibersite and cohenite crystals are still monocrystalline, and there are no reaction rims around them. The troilite is micromelted , usually to a somewhat larger extent than is present in I-III. Severe shear zones, 100-200 J1 wide , cross the entire specimens. They are wavy, fan out, coalesce again , and may displace taenite, plessite and minerals several millimeters. The present exterior surfaces of the slugs and wedge-shaped masses have no doubt been produced in a similar fashion by shear-rupture and have later become corroded. Figure 469. Canyon Diablo (Copenhagen no. 18463). Shock­ The taenite rims and lamellae are dirty-brownish, with annealed stage VI . Typical matte structure, with some co henite crystals to the right. Etched. Scale bar 2 mm. low hardnesses, 160-200, due to annealing. In crossed Nicols the taenite displays an unusual sheen from many small crystals, each 5-10 J1 across. This kind of material is believed to represent shock­ annealed fragments of the impacting main body. Since the fragments have not had a very long flight through the atmosphere, well developed fusion crusts and heat-affected rim zones are not expected to be present. The energy responsible for bulk reheating of the small masses to about 600° C is believed to have come from the conversion of kinetic to heat energy during the impact and fragmentation.
    [Show full text]
  • Nonchondritic Meteorites Posters
    Lunar and Planetary Science XXXIX (2008) sess608.pdf Thursday, March 13, 2008 POSTER SESSION II: NONCHONDRITIC METEORITES 6:30 p.m. Fitness Center Greenwood R. C. Franchi I. A. Gibson J. M. How Useful are High-Precision Δ 17O Data in Defining the Asteroidal Sources of Meteorites?: Evidence from Main-Group Pallasites, Primitive and Differentiated Achondrites [#2445] High-precision oxygen isotope analysis is capable of revealing important information about the relationship between different meteorite groups. New data confirm that the main-group pallasites are from a distinct source to either the HEDs or mesosiderites. Dobrica E. Moine B. Poitrasson F. Toplis M. J. Bascou J. Rare Earth Element Insight into the Petrologic Evolution of the Acapulcoite-Lodranite Parent Body [#1327] In this study we present petrological and geochemical constraints on the evolution of the acapulcoite-lodranite (A-L) parent body with emphasis on new rare earth element (REE). Bascou J. Dobrica E. Maurice C. Moine B. Toplis M. J. Texture Analysis in Acapulco and Lodran Achondrites [#1317] EBSD-measured lattice-preferred orientation of minerals of both Acapulco and Lodran achondrites have been analyzed and combined with petrological and geochemical investigations providing new constraints on the melt extraction and migration processes. Rumble D. III Irving A. J. Bunch T. E. Wittke H. J. Kuehner S. M. Oxygen Isotopic and Petrological Diversity Among Brachinites NWA 4872, NWA 4874, NWA 4882 and NWA 4969: How Many Ancient Parent Bodies? [#1974] Brachinites, related ultramafic achondrites and Graves Nunataks 06128 may derive from an incompletely-heated, heterogeneous “planetary” parent body. Petitat M. Kleine T. Touboul M.
    [Show full text]
  • Texture, Chemical Composition and Genesis of Schreibersite in Iron Meteorite
    Title Texture, Chemical Composition and Genesis of Schreibersite in Iron Meteorite Author(s) Yoshikawa, Masahide; Matsueda, Hiroharu Citation 北海道大学理学部紀要, 23(2), 255-280 Issue Date 1992-08 Doc URL http://hdl.handle.net/2115/36782 Type bulletin (article) File Information 23-2_p255-280.pdf Instructions for use Hokkaido University Collection of Scholarly and Academic Papers : HUSCAP Jour. Fac. Sci ., Hokkaido Univ., Ser. IV, vol. 23, no. 2, Aug., 1992. pp. 255 -280 TEXTURE, CHEMICAL COMPOSITION AND GENESIS OF SCHREIBERSITE IN IRON METEORITE by Masahide Yoshikawa* and Hiroharu Matsueda (with 13 text-figures, 9 tables and 3 plates) Abstract Thirteen iron meteorites composed of Hexahedrite, Octahedrite and Ataxite were investigated to estimate their cooling history and origin. They are mainly composed of Fe-Ni metals (kamacite and taenite) with smaller amounts of schreibersite (Fe, Ni)3P and sulfides (troilite and sphalerite) . Schreibersite occurs an idiomorphic and xenomorphic crystals and its mode of occurrence is variable in iron meteorites. Xenomorphic schreibersite is subdivided into 6 types on the basis of their textures and relationships with coexisting minerals. Chemical composition of schreibersite varies from 20 to 40 atom. % Ni with textural types among some iron meteorites with different bulk chemical compositions and even in the same meteorite (e. g. Canyon Diablo), while it does not vary so clear with textural types in ALH - 77263. Schreibersite seems to maintain a local equilibrium with coexisting metal phases. Based on the Fe- Ni- P phase diagram, it is estimated that xenomorphic and coarse-grained schreibersite in Y- 75031 and in DRPA 7S007 were crystallized from stability field of taenite and schreibersite at about SOO°C under rapid diffusion conditions.
    [Show full text]
  • Thermal Equilibration of Iron Meteorite and Pallasite Parent Bodies Recorded at the Mineral Scale by Fe and Ni Isotope Systematics
    Available online at www.sciencedirect.com ScienceDirect Geochimica et Cosmochimica Acta 217 (2017) 95–111 www.elsevier.com/locate/gca Thermal equilibration of iron meteorite and pallasite parent bodies recorded at the mineral scale by Fe and Ni isotope systematics Stepan M. Chernonozhkin a,b, Mona Weyrauch c, Steven Goderis a,b,⇑, Martin Oeser c, Seann J. McKibbin b, Ingo Horn c, Lutz Hecht d, Stefan Weyer c, Philippe Claeys b, Frank Vanhaecke a a Ghent University, Department of Analytical Chemistry, Campus Sterre, Krijgslaan 281–S12, 9000 Ghent, Belgium b Vrije Universiteit Brussel, Analytical, Environmental, and Geo-Chemistry, Pleinlaan 2, 1050 Brussels, Belgium c Leibniz Universita¨t Hannover, Institute of Mineralogy, Callinstrasse 3, 30167 Hannover, Germany d Museum fu¨r Naturkunde, Leibniz Institute for Evolution and Biodiversity Science, Invalidenstrasse 43, 10115 Berlin, Germany Received 6 January 2017; accepted in revised form 9 August 2017; Available online 19 August 2017 Abstract In this work, a femtosecond laser ablation (LA) system coupled to a multi-collector inductively coupled plasma-mass spec- trometer (fs-LA-MC-ICP-MS) was used to obtain laterally resolved (30–80 lm), high-precision combined Ni and Fe stable isotope ratio data for a variety of mineral phases (olivine, kamacite, taenite, schreibersite and troilite) composing main group pallasites (PMG) and iron meteorites. The stable isotopic signatures of Fe and Ni at the mineral scale, in combination with the factors governing the kinetic or equilibrium isotope fractionation processes, are used to interpret the thermal histories of small differentiated asteroidal bodies. As Fe isotopic zoning is only barely resolvable within the internal precision level of the isotope ratio measurements within a single olivine in Esquel PMG, the isotopically lighter olivine core relative to the rim 56/54 (D Ferim-core = 0.059‰) suggests that the olivines were largely thermally equilibrated.
    [Show full text]
  • TRACE ELEMENT COMPOSITION and CLASSIFICATION of Ni-RICH ATAXITE ONELLO
    81st Annual Meeting of The Meteoritical Society 2018 (LPI Contrib. No. 2067) 6176.pdf TRACE ELEMENT COMPOSITION AND CLASSIFICATION OF Ni-RICH ATAXITE ONELLO. K. D. Litasov1,2, A. Ishikawa3, A. G. Kopylova4, N. M. Podgornykh1, 1Sobolev Institute of Geology and Mineralogy, SB RAS, 3 Koptyuga Ave, Novosibirsk, 630090, Russia ([email protected]); 2Novosibirsk State University, 2 Pirogova st, Novosibirsk 630090, Russia; 3Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo, 152- 8550, Japan; 4Institute of Diamond and Precious Metal Geology, 39 Lenina Ave, Yakutsk, 677980, Russia Introduction: Significant amount of iron meteorites remains poorly described and ungrouped. Some of them re- veal anomalous composition, which do not allow classification to the specific known groups [1]. Here we provide new data on the unique Ni- and P-rich iron meteorite Onello, which contains rare high-pressure phosphide allabogdanite [2]. Onello was found in Yakutia (Russia) in 1997. Preliminary study did not allow its clear classification [3]. Methods: Several 0.5-2 cm fragments of meteorite were cut and polished for investigation by scanning electron microscope (Tescan MYRA 3 LMU) with energy-dispersive system X-Max-80 (Oxford Instr.). Trace elements com- position was obtained by LA-ICP-MS (Thermo Scientific Element XR) method at University of Tokyo (Japan). We used homogenous piece of Campo del Cielo iron and synthetic FeNi-metal [4] as standards. Results and discussion: Onello is fine-grained ataxite with matrix consisting of taenite with 23.0-25.4 wt% Ni. Taenite matrix contains numerous tiny inclusions of schreibersite (22-26 wt% Ni), nickelphosphide (44-52 wt% Ni) and allabogdanite (20.6-21.8 wt% Ni).
    [Show full text]
  • (2000) Forging Asteroid-Meteorite Relationships Through Reflectance
    Forging Asteroid-Meteorite Relationships through Reflectance Spectroscopy by Thomas H. Burbine Jr. B.S. Physics Rensselaer Polytechnic Institute, 1988 M.S. Geology and Planetary Science University of Pittsburgh, 1991 SUBMITTED TO THE DEPARTMENT OF EARTH, ATMOSPHERIC, AND PLANETARY SCIENCES IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY IN PLANETARY SCIENCES AT THE MASSACHUSETTS INSTITUTE OF TECHNOLOGY FEBRUARY 2000 © 2000 Massachusetts Institute of Technology. All rights reserved. Signature of Author: Department of Earth, Atmospheric, and Planetary Sciences December 30, 1999 Certified by: Richard P. Binzel Professor of Earth, Atmospheric, and Planetary Sciences Thesis Supervisor Accepted by: Ronald G. Prinn MASSACHUSES INSTMUTE Professor of Earth, Atmospheric, and Planetary Sciences Department Head JA N 0 1 2000 ARCHIVES LIBRARIES I 3 Forging Asteroid-Meteorite Relationships through Reflectance Spectroscopy by Thomas H. Burbine Jr. Submitted to the Department of Earth, Atmospheric, and Planetary Sciences on December 30, 1999 in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Planetary Sciences ABSTRACT Near-infrared spectra (-0.90 to ~1.65 microns) were obtained for 196 main-belt and near-Earth asteroids to determine plausible meteorite parent bodies. These spectra, when coupled with previously obtained visible data, allow for a better determination of asteroid mineralogies. Over half of the observed objects have estimated diameters less than 20 k-m. Many important results were obtained concerning the compositional structure of the asteroid belt. A number of small objects near asteroid 4 Vesta were found to have near-infrared spectra similar to the eucrite and howardite meteorites, which are believed to be derived from Vesta.
    [Show full text]
  • Proceedings of the United States National Museum
    PROCEEDINGS OF THE UNITED STATES NATIONAL MUSEUM SMITHSONIAN INSTITUTION U. S. NATIONAL MUSEUM Vol. 107 Washington : 1958 No. 3388 STUDIES OF SEVEN SIDERITES By Edward P. Henderson and Stuart H. Perry Introduction These seven descriptions are some of the investigations the authors made between 1940 and 1956. Some of these observations formed the background study to U. S. National Museum Bulletin 184, by S. H. Perry, published in 1944. After that volume was published, a limited number of albums of photomicrographs on non meteorites with interpretations were also privately published by S. H. Perr^^ and given a limited distribution. These nine volumes are now available in the following mstitutions: American Museum of Natural History; Chicago Museum of Natmal History; Mineralogical Museum, Harvard University; U. S. National Musemn; Mineralogical Museum, Uni- versity of Michigan; and British Museum (Natural History). During these studies our findings sometimes differed from the data that others had published on the same meteorites, and we suggested that a reexamination should be made. The divergences were found in the descriptions of specimens, chemical analyses, the assignment of types and the identifications of conspicuous minerals. 339 340 PROCEEDINGS OF THE NATIOlSrAL MUSEUM vol. 107 Some of these findings confirm data published b}'- others and some correct errors in earlier descriptions. Two of the studies are descrip- tions of undescribed irons. The undescribed meteorites are the Goose Lake, California, and the Keen Mountain, Virginia, irons. The former was found in 1938, and although it had been pictured in several publications, its unique surface features were not described properly. The Keen Mountain iron was found in 1950 and is not as well known.
    [Show full text]
  • Barringerite from the Santa Catharina Ungrouped Iron Meteorite
    Lunar and Planetary Science XXXIV (2003) 1681.pdf BARRINGERITE FROM THE SANTA CATHARINA UNGROUPED IRON METEORITE. F. Brandstätter1, M. A. Nazarov2 and G. Kurat1. 1Naturhistorisches Museum, Postfach 417, A-1014 Vienna, Aus- tria, ([email protected]) 2Vernadsky Institute of Geochemistry and Analytical Chemistry, Moscow 119991, Russia. Introduction: Barringerite, (Fe,Ni)2P, is a rare Co-rich and have a Ni content of about 20 wt%. Bar- higher phosphide, which has been reported only from ringerites of CM chondrites have variable Ni and Co the Ollague (Imilac) pallasite [1], the lunar meteorite contents but when they are Co-rich they are also rich Y 793274 [2], some CM chondrites [e.g., 3], and the in Ni (Fig. 4). In addition, the barringerites from CM oxidation zone of a Cu-Ni sulfide deposit in China [4]. chondrites contain commonly some S, Cr and Ca, Phase diagrams predict that barringerite can not stably elements that are absent in the Santa Catharina and co-exist with Fe,Ni metal and should react with the Onello barringerites. Pallasite Ollague (Imilac) and latter to produce schreibersite [5]. In fact, barringerite lunar meteorite Y 793274 contain low-Co barringerite has never been observed to co-exist directly with Fe,Ni (Fig. 4). Schreibersite in Santa Catharina shows a metal, except for a recently described occurrence in large compositional range: Fe 32-57, Ni 28-49, Co the Onello iron [6]. In this contribution we report on 0.14-0.82 (wt%) with a Co-Ni anti-correlation (Fig. 4) the forbidden barringerite-metal association in the and a constant P content of 15.6 (0.17) wt%.
    [Show full text]
  • An Electron Microscope Investigation of Eight Ataxite and One Mesosiderite Meteorites
    Lehigh University Lehigh Preserve Theses and Dissertations 1-1-1981 An electron microscope investigation of eight ataxite and one mesosiderite meteorites. Paul M. Novotny Follow this and additional works at: http://preserve.lehigh.edu/etd Part of the Materials Science and Engineering Commons Recommended Citation Novotny, Paul M., "An electron microscope investigation of eight ataxite and one mesosiderite meteorites." (1981). Theses and Dissertations. Paper 1944. This Thesis is brought to you for free and open access by Lehigh Preserve. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of Lehigh Preserve. For more information, please contact [email protected]. AN ELECTRON MICROSCOPE INVESTIGATION OF EIGHT ATAXITE AND ONE MESOSIDERITE METEORITES by Paul M. Novotny A Thesis Presented to the Graduate Committee of Lehigh University in Candidacy for the Degree of Master of Science in Metallurgy and Materials Engineering Lehigh University 1981 ProQuest Number: EP76217 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest ProQuest EP76217 Published by ProQuest LLC (2015). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code Microform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 CERTIFICATE OF APPROVAL This thesis is accepted in partial fulfillment of the requirements for the degree of Master of Science.
    [Show full text]
  • Coo-38 2- 56 Rare Gas Evidence for Two Paired Meteorite
    COO-38 2- 56 RARE GAS EVIDENCE FOR TWO PAIRED METEORITE FALLS Dieter Heymann / . Enrico Fermi Institute for Nuclear Studies,, I ,! University of Chicago, Chicago, Illinois, 60637 F-Submitted to et Cosmochimic May 1965 ,/ , NASA Grant NsG-366 Research AE€ Contract AT (11-1)-382 EFINS 65-53 Rare Gas Evidence for Two Paired Meteorite Falls Dieter Heymann Enrico Fermi Institute for Nuclear Studies University of Chicago, Chicago, Illinois Abstract. Rare gas contents were determined by mass- spectrometry in meteorites of two so-called paired falls: Accalana-Artracoona-Carraweena and La Lande-Melrose-Taiban. The results show that Accalana and Carraweena Zre identical, whereas Artracoona appears to be an independent fall. The "La Lande" group includes at least one independent fall: Taiban. A comparison of terrestrial meteorite ages to meteorite fall frequencies shows, that the survival of coin- cidences of octahedrites and ordinary chondrites, is quite likely. ******* Among the thousands of meteorite finds on Earth, there are several instances in which chemically and structurally similar meteorites were recovered from the same area. Such a situation arises for instance when a meteorite shower occurs; the famous L'Aigle shower of 1803 deposited 2000-3000 stones in an area of approximately 12 x 4 km (Heide, 1964). While showers of this magnitude are exceptional, it is nevertheless true that a majority of stone meteorites break up during their fall through the atmosphere so that the fall of a single stone -2- is about as rare an event as the occurence of a shower. The fall of several fragments from one meteoroid is by no means restricted to stones, but has been observed for irons as well (e.g.
    [Show full text]
  • Handbook of Iron Meteorites, Volume 3 (Toluca – Tombigbee River)
    Tlacotepec - Toluca 1209 troilite and daubreelite, each 1-5 J.1 thick. When different 1952. It is likely that these collectors more or less absorbed troilite-daubreelite nodules in the same section are com­ the specimens discovered by the immediately preceding pared, the daubreelite lamellae show random orientation, generation while they were tilling fields. It may be i.e., the troilite orientation with respect to the parent estimated that Kranz, Ward and Foote purchased 100, 500 austenite crystal is also random. and 300 kg, respectively , while Nininger (1952b) reported A few troilite-daubreelite intergrowths have assumed that he acquired 325 and 180 kg in 1929 and 1952, plate shapes and reach dimensions of 500 x 1 J.1 in cross respectively. If we add to this the weight of the collection section. They are enveloped in 1-2 J.1 wide creamcolored of specimens in Mexico City, i.e., about 900 kg which has austenite, bordered on either side by 10-15 J.1 wide martens­ not passed through the hands of the foreign collectors, and itic-bainitic zones. an additional 500 kg representing the material collected by No silicates, graphites or carbides were detected in the Humboldt, Stein, Burkart and minor dealers, we end up sections. with a total of about 2.8 tons as an estimate of what has Tlacotepec is a nickel-rich ataxite of group IVB which actually been removed from the Toluca region. To this we is closely related to lquique, Hoba and Cape of Good Hope. must add the numerous fragments which have been forged However, it appears to be slightly less weathered than these.
    [Show full text]