Handbook of Iron Meteorites, Volume 2
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554 Ector County -- Edmonton (Canada) shape that the mass had when circling in cosmos, except for Ector County, Texas, U.S.A. the truncated, rounded portions which were ablation sculptured during penetration of the atmosphere. In other A mass of perhaps 25 kg, briefly mentioned by La Paz (1944 : 302), words, it appears that Edmonton at an early time was was assumed to be an independent meteorite and labeled Ector dislodged from its "matrix" in the form of a boxlike, cubic County. I have examined a 75 g sample cut from the mass (Chicago no. 2388) and found it to be a typical Odessa specimen. Other cleavage fragment, which was only little modified during samples in Chicago, each of about 0.5 kg weight (nos. 2329, 2330, the atmospheric flight . 2331), were so weathered that they might be termed shale-balls, An etched section shows that Edmonton is a normal co nsisting of rather massive limonite with only minute amounts of uncorroded metal. The Odessa Crater with its numerous associated hexahedrite, a monocrystal with Neumann bands from rim iron fragments, some of them thoroughly weathered, lie s in Ector to rim. In the heat-affected zone they are replaced by County, so it is confusing to retain Ector County as an individual 50-200 J.1 serrated o:2 grains, in the outermost 0.2 mm of iron meteorite. Consequently, it should be deleted, and all material so labeled transferred to Odessa. which may be found micromelted phosphides. It can be Edmonton (Canada), Alberta, Canada 53° 40'N, 113°25'W Hexahedrite, H. Single crystal of ferrite, larger than 15 em. Decorated Neumann bands. HV I 25 ±5. Group IIA . 5.37% Ni , about 0.2% P, 60.4 ppm Ga, 172 ppm Ge, 33 ppm Ir . HISTORY The mass of 7.34 kg was first recorded by A.D. Nininger (1940). According to a report in the Smithsonian Figure 745. Edmonton (Canada). Main mass in University of Institution from Professor John A. Allan, Department of Alberta, Edmonton. Note the box shape. Ruler in in ches. (Courtesy Geology, University of Alberta, Edmonton, the mass was P.M. Millman.) plowed up 6-10 km north of Edmonton and 3-6 km east of the road to the Namao Airport. The location is in the east half of Township 54, Range 24, west of the fourth meridian, and the approximate coordinates are given above. The mass was apparently found in the early thirties and was in private possession until it was acquired by Professor Allan for the University of Alberta in 1938. Bauer (I 963) found a very low amount of helium isotopes, lower than in any other of the 34 irons, examined by him. COLLECTIONS Main mass in University of Alberta , Edmonton. Washington (584 g). DESCRIPTION The mass has the average dimensions of 15 x 12 x 10 em and is partly bordered on four sides by cubic cleavage planes so that the exterior appearance approxi mates a truncated box. It is covered with 0.1-1 mm Figure 746. Edmon ton (Canada) (U .S .N .M. no. 1634 ). The adhering oxide scales, but an etched section discloses that a Neumann bands are para llel to (2llla and indicate that the exterior faces are (l OO)a cleavage faces. Some imperfect cleavage fi ssures 1-1.5 mm continuous heat-affected o: 2 zone is well-pre run horizontally across the picture. The heat-a ffec ted or 2 zone is served. It is extremely interesting, then, that the exterior di stin ctly developed around the whole per iphery. Deep-etched. cube form as we see it now probably closely resembles the Scale bar 2 em. S.I . neg. 259. EDMONTON (CANADA) - SELECTED CHEMICAL ANALYSES percentage ppm Reference Ni Co P c s Cr Cu Zn Ga Ge Ir Pt Wasson 1969 5.37 60.4 172 33 Edmonton (Canada) - Edmonton (Kentucky) 555 concluded from this that the mass on the average has lost Edmonton (Canada) is a typical hexahedrite which only a 0 .5- 1 rum thin skin by corrosion. The Neumann closely resembles Scottsville, as described by Buchwald bands on this particular section follow six directions, (1967a: figures 53-57). It further resembles Bennett divided in three sets which are mutually perpendicular; it County, Bruno, and Angra dos Reis. can be shown that the only case where the traces of the (211) Neumann bands occur in this configuration is on a Specimen in the U.S. National Museum in Washington: cube face of the kamacite; see for example Spencer (1951). 584 g slice (no. 1634, 10 x 8 x 0.9 em) The Neumann bands are discontinuous and partly resorbed due to some slight reheating, but recrystallization has not Edmonton (Kentucky), Kentucky, U.S.A. started. Some are decorated with 0.5-2 11 rhabdites. The 36°59'N, 85°34'W; 300m microhardness of the kamacite is 125±5, but increases steeply to 175±20 in the heat-affected rim zone (hardness Polycrystalline, fine octahedrite, Of. Bandwidth 0.32±0.05 mm. curve type III). Edmonton belongs to the softest meteorites Neumann bands. HV 230± 15. ever recorded, and it must have been thoroughly annealed Group III C. 12.65% N i, 0.70% Co, about 0.3% P, 24 ppm Ga, during its cosmic sojourn. A 5.4% Ni - 0.2% P alloy will 34 ppm Ge , 0.55 ppm Ir. only in its annealed state exhibit as low a hardness as 125; HISTORY compare Buchwald 1966: figures 13-15. A mass of 10.2 kg was plowed up in 1942 on the farm In six different places of the section cubic cleavage of Samp Johnson, about 7 km east of Edmonton, Metcalfe planes parallel to the exterior surfaces stand in contrast County. It was acquired by the U.S. National Museum in because they are easily attacked by corrosion and are now 1943 as a gift from Stuart H. Perry, and it was described filled with thin oxide veinlets. This characteristic is a with an analysis and photomicrographs by Henderson & diagnostic for the cube planes in hexahedrites and may help Perry (1947 ). One end had been heated with a blowtorch to orient any hexahedrite. by the finder in order to detach a specimen, but the Schreibersite was not identified on 100 cm2 , but metallographic examination showed that the damage to the rhabdites in form of 5-20 11 thick, tetragonal prisms, are mass was very local. By now about 10 slices, each 6-8 rum very common. Rhabdite plates, typically 10-20 11 thick and thick, have been cut from this end. Uhlig (1954) repro 0 .5-2 rum large , are also common. They are monocrystalline duced two of the photographs given by Henderson & Perry, and distorted only a little, if at all . while Mason (1962a: fig ure 54) and Wood (1968: figure 3) Troilite occurs as scattered 1-4 rum nodules that are gave photomacrographs of two other slices to demonstrate composed of 5-10 11 grains due to shock melting. Locally, the extremely well developed Widmanstatten structure. an aggregate of 200 J.1 daubreelite with tiny troilite and Agrell et al. (1963) found a nickel depletion in the metal grains inside is seen . Two irregular, lobed grains 800 x kamacite close to the taenite interphase, and Reed 200 11 were suspected to be cohenite, but they disappeared (1965a,b) determined the composition of the kamacite, during repolishing before the identification could be fully taenite and schreibersite. Short & Andersen (1965) also confirmed under the microprobe. examined Edmonton with the electron microprobe. The general appearance of the etched section is mottled; bright and matte patches alternate in an irregular COLLECTIONS way. Under high magnification it is seen that the main Washington (8,275 g), Moscow (300 g), Sydney reason for this is the varying concentration of small (265 g), La Jolla, School of Engineering (257 g), Madrid rhabdites. (246 g) , Harvard (165 g), Chicago (151 g). EDMONTON (KENTUCKY) - SELECTED CHEMICAL ANALYSES percentage ppm References Ni Co p c s Cr Cu Zn Ga Ge Ir Pt Henderson & Perry 1947 12.57 0.79 Goldberg eta!. 1951 12.68 0.73 24.7 Lovering et al. 1957 0.57 I 1.7 396 22 26 Nichiporuk & Brown 1965 I 0 .6 0.5 Wasson & Kimberlin 1967 12.7±0.3 I 25.4 34.6 0.55 Analyses for phosphorus and carbon are needed. 556 Edmonton (Kentucky) DESCRIPTION intergrowths of lobed cubic carbides and I-5 11 taenite The mass has the approximate overall dimensions 24 x grains. The "roses" do occasionally increase to a volume of II x 8 em, but it is more irregular and distorted in its shape 4 x 4 x 4 mm resembling a cavernous sponge. They are than most irons; and this is not due to corrosion, since the particularly easy to identify upon a deep-etched section heat-affected a- 2 zone is preserved as a continuous rim. The where they appear as shiny, white patches on a dark, shape resembles a piece of modern, nonfigurative art with plessitic background. Their immediate surroundings are knobs, noses and large , irregular indentations; no deep holes spheroidized plessite with 2-IO 11 taenite spherules, or or cavities are present. There is no evidence on the surface pearlitic plessite with 0.5-111 wide taenite lamellae . The or on the slices that Edmonton should have fragmented in carbide roses have hardnesses ranging from 600 to 900, the atmosphere. It rather represents another extreme in depending upon the amount of inclusions. The adjacent atmospheric sculpturing, widely different from the flat duplex plessite is much softer, about 260-300.