960 Paloduro - Pan de Azucar

A mass of 3 kg was found in 1935 near Paloduro, Armstrong County (A .D. Nininger 1937). According to Barnes (1939a: 598), the main mass of 2,826 g, apparently an octahedrite, is in Texas Observers Collection, Fort Worth, but the material is undescribed.

Pan de Azucar, Atacama, Chile

Approximately 26°S, 70°W

Coarse octahedrite, Og. Bandwidth 2.2±0.5 mm. Neumann bands. HV 180±5.

Group I. About 6.8% Ni, 0.18% P, 82 ppm Ga, 308 ppm Ge, 2.0 ppm Jr.

Carrizalillo is probably a fragment of the Pan de Azucar shower.

HISTORY

A mass of about 20.3 kg was found in 1887 in the Atacama Desert. The locality was repo rted to be 67 miles from the small port of Pan de Azucar (Fletcher 1908).

The complete mass was purchased by the British Museum, from which a few small sections have been distributed. Smales et a!. (1967), who determined the trace e lements, found Pan de Azucar similar to Youndegin and five other, typical group I irons. As discussed below (page 961), the Pan de Azucar fall comprises another mass, previously known as Carrizalillo.

COLLECTIONS

London ( 19.28 kg main mass and 91 g slice), Chicago (210 g) , Washington (101 g), Calcutta (92 g) .

DESCRIPTION

The main mass in London is undescribed. The slice in the U.S . National Museum shows, however, that it must be in quite good shape, since regmaglypts, 2-3 em in diameter, are present ; and the fusion crust is preserved in protected places, albeit somewhat rusty. The e tched section confirms that the iron has suffered very little from weathering. The heat-affected a2 zone is found as a 1-2.5 mm wide rim under most of the surfaces, and micromelte d phosphides are present in the exterior 0.5-1 mm of the zone , indicating that, at the most, 0.5 mm has been removed by corrosion. The rhabdites are frequently connected with 1 J1 wide veinlets of phosphide melts. The microhardness of the a2

zone is 200± 10. Pan de Azucar is a coarse octahedrite which shows

straight, but swollen (~ ~ 10), kamacite lamellae with a

width of 2.2±0.5 mm. Local grain growth, which has eliminated the straight Widmanstatten boundaries, is responsible for the swollen, irregular appearance of the lamellae , and in places it has created polyhedric grains, 5-10 mm across. The kamacite has subboundaries, decor­ated with 0.5-2 J1 rhabdites; and Neumann bands are very common . The microhardness of the kamacite is 180±5.

Taenite and plessite cover 2-3% by area. The fields are, as usual, situated in the lamella boundaries but, due to the a-grain growth, may also be completely embedded in a kamacite grain of uniform orientation. Comb plessite and acicular plessite are the most common forms, and tarnished taenite (HV 370±30) occurs everywhere . Spheroidized and pearlitic plessite were not observed but may be present in other cohenite-rich sections. The acicular plessite has a grid of characteristic pointed kamacite platelets, each 5-10 f.1

thick. As usual, the tarnished taenite loses its bluish-gray tint in the heat-affected a2 zone. It is here bordered by 10-20 J1 wide bainite-martensite rims, presumably because carbon redistributed itself by the brief atmospheric reheating.

Schreibersite is common as 20-80 J1 wide grain bound­ary precipitates and as 5-25 J1 blebs inside the plessite fields, but no large crystals were observed on 80 cm2 • Rhabdites are very common, ranging from 1-30 J1 in size, with the majority being prisms about 10 J1 thick. The bulk phos­phorus content is estimated to be 0.15-0.20%.

Figure 1347. Pan de Azucar. The Carrizalillo specimen (Oslo). A coarse octahedrite of group I. Taenite and plessite bands appear dark . Two fissures that follow cubic cleavage planes of the kamacite a re at the right. Grain boundaries, subboundaries, rhabdites and Neumann bands are prominent, as usual, in group I. Etched. Scale bar 500 !J. .

PAN DE AZUCAR - SELECTED CHEMICAL ANALYSES

References

Smales et al. 1967 Wasson , 1971,

pers. comm. Crocket 1972

percentage Ni Co P

6.84

c s Cr Cu

13.0 172

ppm Zn

15 .1

Ga

82

82.1

Ge

308

308

Ir

2.0 2.8

Pt

8.9

Cohenite, troilite, silicates and graphite were not observed but are expected to be found in other sections. Locally, at the surface, the linear elements of the structure are heavily distorted and bent. It appears to be postatmos­pheric and is probably due to hammering by the discoverer.

Pan de Azucar has a microstructure which closely resembles the structure of inclusion-poor specimens of Canyon Diablo, Magura and Youndegin. This, in connection with the trace-element composition, is sufficient to classify Pan de Azucar as a normal member of the coarse group I meteorites, probably most closely related to Youndegin and Ozren. Below, another part of the Pan de Azucar material, Carrizalillo, is treated in greater detail.

Specimen in the U.S. National Museum in Washington:

101 g slice (no. 1558, 9 x 5.5 x 0.3 em)

Pan de Azucar (Carrizalillo), Atacama, Chile

Approximately 26°S, 70°W

Coarse octahedrite, Og. Bandwidth 2.2±0.4 mm Neumann bands. HV 178±5.

Group I. About 6.8% Ni, 0.18% P, 81 ppm Ga, 328 ppm Ge, 1.1 ppm Jr.

The meteorite is distinctly different from Copiapo. It is probably a fragment of the Pan de Azucar shower.

HISTORY

According to Wiilfing (1897: 86 and 87), a mass of I ,328 g was sent by director L. Sundt, who had been employed at a mining office in Atacama for 23 years, to the University Museum in Kristiania (Oslo) in I884. Since no fu(ther details were known, Wiiifing provisionally listed the mass as a Copiapo specimen. In later catalogs the meteorite has been entered under various headings. In the latest edition of Prior's Catalog (Hey I966 : II7) it is listed as "Corrizatillo" with uncertain coordinates and unknown structure and composition.

Dr. O.F. Frigstad, curator of the Oslo collection, gave the following information (letter of February I8, 197I ) :

"The Norwegian geologist L. Sundt donated in 1884 two meteorites (Carrizalillo and Galleguillos) to the Univer­sity collection, represented by the then professor Amund Helland. There are no letters preserved, but the original label (for the meteorite in question) read: 'Corrizalillo. North of Copiapo, Atacama, Chile. Gift from L. Sundt, Valparaiso, 1884.' Since there are no places in Atacama by the name Corrizalillo, the most

Pan de Azucar - Pan de Azucar (Carrizalillo) 96I

probable locality is one called Carrizalillo, situated at 26°2's, 70°20'W."

There are at least two other localities by the name Carrizalillo in Atacama, situated at 28° 1 O'S , 69° 46'W and 29°5'S, 71 °20'W, respectively; but, since both of these are situated south of Copiapo while the label expressly states north of Copiapo, the set of coordinates suggested by Frigstad remains the most probable.

The material is undescribed except for a note by Goldschmidt ( 1929) who was concerned with the determin­ation of partition coefficients of Pt, Au and Ag between troilite and nickel-iron. Goldschmidt called his material Caranzatillo, but a comparison of his photomacrograph with the specimen in Oslo shows that it is the same mateQ;tl and that his name was, therefore, a simple misprint or misunderstanding.

COLLECTIONS

Oslo (937 g; 256 g slice; 4 7 g slice).

DESCRIPTION

The original dimensions are unknown, but the original weight entered in the acquisition protocols in Oslo in 1884 was 1,328 g. (By a curious coincidence, the other iron acquired on the same date Galleguillos, weighed almost exactly the same, 1 ,330 g). There are no notes as to whether the material received was a single individual or had been cut from a larger mass.

The following is based upon an examination of a 256 g slice (7 x 5.5 x I em) and a 47 g rectangular box (30 x I6 x I3 mm), both of which were kindly loaned to me by Dr. Frigstad·, Oslo.

I ·

Figure 1348. Pan de Azucar. Carrizalillo (Oslo). Acicular plessite field with cloudy taenite edges. Etched. Scale bar 300 JJ..

PAN DE AZUCAR (CARRIZALILLO) - SELECTED CHEMICAL ANALYSES

Reference

Schaudy & Wasson I971

percentage Ni Co P

6.4±0.5

c s Cr Cu ppm Zn Ga

81.2

Ge

328

Ir Pt

1.1

962 Pan de Azucar (Carrizalillo)

Figure 1349. Pan de Azucar. Carrizalillo (Oslo). Detail of an acicular plessite field. Cloudy taenite edges and acicular high-nickel martens­ite in center. Etched. Scale bar 40 J.L. See also Figure 122.

The 256 g sample is a slice, partly sawed, partly broken from another major portion. It displays natural, somewhat corroded, surfaces on all sides. If we assume that the slice

was taken through the middle of a mass - which was not very irregular in shape - then the dimensions correspond very well to an original weight of 1,328 g. If, on the other hand, the slice does not come from the middle of a mass, the original weight of the entire meteorite may have been anythlng above 1 kg. At the moment we have no means of drawing a conclusion as to whether the Carrizalillo material was an entire meteorite of 1,328 g or a 1,328 g fragment broken from some larger mass .

The sample shows shallow regmaglypts, 1-2 em across. They are modified by a superimposed pattern of corrosion pits which are 2-5 mm across and meet along sharp ridges. The pits are similar to the corrosion pits encountered on other irons from Northern Chile, such as Filomena, Barranca Blanca and Iquique. The corrosive attack has not, however, removed very much of the surface, since the only available full section through the meteorite displays a continuous heat-affected a 2 zone varying between 0.1 and 4 mm in width. It is estimated that the mass has lost, on the average, about 0.5 mm by corrosion . The a 2 zone, which in its outermost parts contains micromelted rhabdites, has a hardness of 190±15. The hardness decreases to a minimum of 145±6 in the recovered transition zone and then

Figure 1350. Pan de Azucar. Carrizalillo (Oslo). A vein with shock-melted sulfides and brecciated schreibersite (large white fragments). The shock-melt is a fine-grained eu_tectic of iron and iron sulfide in which daubreelite fragments (D) are dispersed. Polished. Crossed polars. Scale bar 40 J.L.

increases to I78±5 - typical of the unaffected interior (hardness curve type II).

Etched sections display a coarse Widmanstiitten struc­ture of straight, bulky ( W ~ I 0) kamacite lamellae with a width of 2.2±0.4 mm. Locally, grain growth has created almost equiaxial kamacite grains, 10-I5 mm across . The kamacite is rich in subboundaries with I-2 J.l precipitates, and Neumann bands are well developed. The microhardness is I78±5.

Taenite and plessite cover 2-4% by area. The fields are either developed as comb plessite or, more often, as acicular fields which are penetrated by a large number of bayonet­like a -platelets, 5-IO J.l wide . The retained taenite between the a-platelets is more or less transformed to martensite. A small quantity of pearlitic plessite with I J.l wide 'Y-lamellae and of spheroidized plessite with 5-10 'Y-globules is also present. All taenite rims stain in bluish-brown -colors upon etching and are hard (HV 360±25). In the heat-affected a 2 zone the staining disappears and gives way to a yellow structureless taenite, presumably because the taenite has been homogenized by the brief reheating during atmos­pheric flight.

Schreibersite occurs as a few scattered skeleton crys­tals, up to 3 x 0.5 mm in size, and as 20-100 J.l wide grain boundary veinlets . It also occurs as 5-25 J.l irregular blebs inside the open-meshed plessite fields and as I-I5 J.l

rhabdite prisms throughout the kamacite. The bulk phos­phorus content is estimated to be O.I5-0.20%.

Troilite is present as a large nodule, 22 mm across, from which narrow veiniets of troilite penetrate several centimeters along grain boundaries. The troilite, originally monocrystalline with parallel daubreelite lamellae , is dam­aged by shock. Passive blocks with multiple twinning or undulatory extinction alternate with shear zones of recrys­tallized troilite. Along phase boundaries the troilite is micromelted and rapidly solidified to a fme Fe-Ni-S aggregate.

Figure 1351. Pan de Azucar. Carrizalillo (Oslo). The same vein as in Figure 1350 but in a different place. Some troilite fragments survived unmelted but were deformed and now show undulatory ext inction (T). Polished. Crossed polars. Scale bar 40 IJ. . See also Figure 160.

Pan de Azucar (Carrizalillo) 963

The troilite nodule which, during the primary cooling period, had originally nucleated a continuous rim of 0.5 mm wide schreibersite and a discontinuous rim of 0 .2 mm wide cohenite, had later damaged its envelope of minerals and partly penetrated them along fine fissures. A four centimeter long fissure along schreibersite-rich a -a grain boundaries is filled with a shock melt of troilite up to 400 J.l wide , which must have been squeezed outwards from the major troilite nodule. The melt, in penetrating the grain boundaries , has dispersed the brittle schreibersite minerals which are now found as angular fragments, I-IOOpacross , embedded in the fine-grained troilite . A minute amount of daubreelite fragments is also present. Terrestrial corrosion has slightly changed the breccia - mainly by selectively converting the finely dispersed metallic iron to limonite. At the time of the same shock event, several cubic cleavage cracks, 5-I5 J.l wide, were formed in the kama cite. These are now partly filled with terrestrial corrosion products but -like the before-mentioned fissure - must have existed for countless milenniums as internal cavities in the meteorite while it circled in space.

Cohenite occurs as O.I-0.2 mm wide rim zones on schreibersi te. It is ductile, anisotropic and hard (H ~ 1000); and decomposition to graphite has not begun. Haxonite occurs in minute quantities as 5-20 J.l blebs inside some fields of acicular plessite . Two other minerals, possibly sulfides (one isotropic, brown-black; one anisotropic, bright blue) were noted as 0.1-0.5 mm blebs, but they were not identified. Silicates were not detected.

Carrizalillo is a typical inclusion-rich coarse octahedrite of group I. Its kamacite and troilite morphology indicates that a cosmic event shocked the material, fissured it, and squeezed melted troilite out several centimeters through the adjacent metallic grain boundaries and brittle minerals. Since the troilite, thus, does not represent equilibrium conditions from the primary cooling period, it is ill-advised

A

Figure 1352. Pan de Azucar. Carrizalillo (Oslo). An anomalous part of the shock-melted vein. It penetrates schreibersite (S) which is partly altered. Perhaps the globules are fused phosphides dispersed through an iron-sulfide melt, now partly limonitized by exposure to terrestrial corrosion (black). Etched. Scale bar 40 IJ. .

964 Pan de Azucar (Carrizalillo) -Para de Minas

to analyze it in bulk in order to obtain partition coeffi­cients between troilite and iron-nickel.

Carrizalillo is closely related to, e.g., Cranbourne, Burkett and Canyon Diablo. Its similarity to another North Chilean octahedrite, Pan de Azucar, is still more striking. A critical comparison of the macro- and microstructures, the microhardness , the state of corrosion, and the chemical composition reveals no more difference than what may be reasonably ascribed to sampling variation within the same meteorite.

The localities of discovery are poorly known, but the two meteorites certainly come from the same district. Pan de Azucar reportedly came from a locality 100 km from the coast somewhere along the river ,Pan de Azucar. A railroad runs perpendicular to the coast along this river and ends at a mining town called Carrizalillo about 35 km from the coast. It appears that both meteorites were found somewhat east of Carrizalillo, near the river Pan de Azucar, some time during the 1880s when mining prospectors were very active in this area. Only a very approximate coordinate set can be given for the actual discovery site, 26°S, 70°W. The two masses, which may have been fragments of a small shower, reached European collections through different channels and were listed as individual falls, which in all probability is incorrect. Since Pan de Azucar was described first and is the larger mass, this name must have priority. Corrizatillo is a simple misspelling of a Spanish name and has hardly ever appeared in the literature, so it is suggeste d that the correct spelling, Carrizalillo, be introduced and used from now on.

Finally, another alternative should be considered. The Carrizalillo specimen might be a sample cut or broken from the Pan de Azucar mass before either mass was shipped to Europe. A reexamination of the main mass of Pan de Azucar would probably solve this minor point.

Paneth's Iron. See the Supplement.

Para de Minas, Minas Gerais, Brazil

19°52'S , 44°37'W

Fine octahedrite, Of. Bandwidth 0.33±0.05 mm. Neumann bands. HV 185±10.

Group IVA. 8.04% Ni, 0.36% Co, 0.07% P, 2.1 ppm Ga, 0.13 ppm Ge, 2.4 ppm Ir.

HISTORY

A mass of 112 kg was found on the ranch Palmital 12 km southwest of Pani de Minas, in the district of lgaratinga. It was briefly mentioned by Oliveira (1938) and was later described by Curvello & Ferreira (1952) , who presented several photographs and a good analysis. These authors stated that the iron had been seen to fall in 1934, but, as shown below, this is really out of the question. Fireman& Schwarzer (1957) measured the 3 Li, 3 He and 3 H of the meteorite and presented their results on cosmic radiation age under the erroneous assumption that the meteorite fell in 1934. Tilles & Tamers ( 1963) discussed the tritium retention in iron meteorites for a number of falls, including Para de Minas as an accepted fall.

COLLECTIONS

Rio de Janeiro, National Museum (101.9 kg main mass and 500 g slice) , Sao Paolo University (8 kg), Tempe (347 g), Washington (223 g).

DESCRIPTION

The main mass is angular and roughly in the shape of a dog's head. It measures 40 x 30 x 24 em and displays a roughly cut surface at the muzzle end of 21 x 11 em. The mass is rather smooth without regmaglypts and it is corroded. A troilite nodule , 21 mm across, is situated flush with the surface, an indication that many millimeters of the surface have been lost to weathering.

Sections display an irregular 1-5 mm thick crust of terrestrial oxides, below which the corrosive attack goes at least 10 mm in depth, following grain boundaries and particularly dissolving the kamacite phase of the duplex plessite fie lds. No fusion crust and no heat-affected a2 zone can be found, indicating that at least a 2 mm thick surface

Figure 1353. Para de Minas (fempe no. 604.1). A fine octahedrite of group IVA. Deep-etched. Scale in centimeters. (Courtesy C.B. Moore.)

PARA DE MINAS - SELECTED CHEMICAL ANALYSES

percentage ppm References Ni Co p c s Cr Cu Zn Ga Ge Ir Pt

Curvello & Ferreira 1952 7 .87 0.36 0.07 540

Cobb 1967 8.12 0.37 148 2 2.4 Moore et al. 1969 8 .1 9 0.35 0 .06 30 65 140 Schaudy et a!. 1972 7.99 2.21 0.125 2.3

layer has been destroyed by weathering. An attack of this character upon an almost inclusion-free, fine octahedrite requires, I estimate, many thousands of years of exposure to a terrestrial environment. I believe that it is out of the question that the mass fell in 1934, and I suspect that the fragmentary character at one end reported by Curvello & Ferreira (1952), may be an indication of the discoverer's attempt to chisel off material.

The etched sections reveal a fine Widmanstiitten structure of .straight , long (W ~ 50) kamacite lamellae with a width of 0.33±0.05 mm . The kamacite has Neumann bands and subboundaries almost free of precipitates -evidently because the phosphorus content is very low. The microhardness of the kamacite is 185±10; and there is no hardness gradient towards the surface, again indicating that a transitional zone of 3 mm or more has been removed by corrosion . The kamacite is cracked in numerous places; it appears that the fissures follow cubic cleavage planes. The fissures are normally 100-500 J.L long, but only 1-2 J.L wide, and they are partially filled with terrestrial oxidation products. I have noted fissures of this type in quite a number of iron meteorites and believe that they, in general, are preatmospheric and may have originated simultaneously with the Neumann bands. Taenite and plessite cover about 50% by area and display morphologies typical of group IVA. Comb and net plessite prevail, mostly with continuous taenite rims; and cellular plessite, as defined under Gibeon and Chinautla, is also common. Some taenite wedges have martensitic interiors, some show martensitic transition zones and a duplex interior of fine-grained a and "f.

Phosphides are almost absent, in harmony with the analyses. Locally , particularly in the grain boundaries, a few schreibersite blebs, 5 x 2 J.L in size, may be seen; but one has to work with a good polished section to identify them.

Sulfides occur with a frequency of about one per 10 cm2 as lenticular nodules that range from 0.2-3 mm across. They are composed of monocrystalline troilite with 10-15% daubreelite, exsolved in parallel , 10-100 J.L wide lamellae. Sulfide nodules smaller than 200 J.L are also quite common ; many of these are also exsolution products but on a very fine scale, being composed of alternating parallel sheets of troilite and daubreelite, each 1 J.L thick.

Curvello & Ferreira (1952) reported euhedral crystals . of chromite , about 0.5 mm across, and associated with troilite.

Para de Minas is a weathered , fine octahedrite that may have a high terrestrial age and certainly did not fall in 1934. It is structurally closely related to Bristol, Charlotte and Gibe on ; and also, chemically, it is almost indistinguishable from these IV A meteorites.

Specimen in the U.S. National Museum in Washington:

223 g part slice (no. 1510 , 8 x 5 x 0.8 em)

Parral. See Morito (Parral Fragment)

Para de Minas - Patos de Minas (hexahedrite) 965

Patos de Minas (hexahedrite), Minas Gerais, Brazil

Approximately 18° 35'S, 46°3 2'W

Hexahedrite, H. Single crystal larger than 16 em across. Neumann bands.

Group IIA. About 5.5% Ni, 0.2% P. Synonym: Corrego Areado.

HISTORY

A mass of 3 2 kg is said to have fallen in 1 925; the date and time are, however, unknown (Guimariies 1 958). From the results below, it may be concluded with certainty that the mass did not fall in 1925, but was an old fall which probably was discovered at that time.

Guimaraes (1958), who presented a brief description with three photographs of the exterior and four photomicro­graphs, gave the site of discovery as the border of C6rrego Areado, in the Patos community. The exact place of discovery could not be located on the available maps, so the coordinates above are for the town of Patos de Minas.

COLLECTIONS

Main mass in Brazil, in the Geological Survey , Belo Horizonte, State of Minas Gerais. Washington (827 g).

ANALYSES

Guimaraes (1958) reported an analysis which although insufficient (5 .29% Ni, 0.07% Co, 0.06% P) indicates the hexahedral nature of the meteorite.

DESCRIPTION

Patos de Minas is an elongated mass somewhat resem­bling the head of an enormous duck. Its length is about 30 em, and the massive part of the "head" is about 21 x 12 em in two perpendicular directions. It is corroded, but some regmaglypts are indistinctly visible as shallow depres­sions, 2-4 em across .

A 16 x 8 x 1 em full slice through the middle of the mass, prepared as a deep-etched section in Brazil , was briefly examined while it was on loan to the Smithsonian Institution in Washington in 1968. It shows that Patos de Minas is a normal hexahedrite with Neumann bands extending across the whole section. In most places the bands reach the corroded surface ; but over short lengths of 1-2 em, irregular 0.5-1 mm wide remnants of a heat­affected a 2 zone may still be recognized. This observation is unambiguous proof that the meteorite has lost about 1-2 mm of its exterior by weathering. It is out of the question, under the given climatic conditions, that this loss can have occurred between its "fall" in 1925 and 1958 when the mass was reported in scientific literature. Thus, Patos already had a significant terrestrial age when it was discovered in 19 25 .

The etched section shows the usual irregular patches of alternating clear and frosty kamacite. In the clear areas the rhabdites are rather large (prisms with 5-30 J.L cross section),

966 Patos de Minas (hexahedrite) - Perryville

Figure 1354. Patos de Minas (U.S.N.M.). A normal hexahedrite of group IIA. Globular and lenticular troilite nodules and light- and dark-shaded areas according to the density and size of the rhabdites. Deep-etched. Scale bar 30 mm. S.l. neg. 1484.

and the Neumann bands are broad, 5-10 J.l. In the fros.ty areas the rhabdites are ten times smaller and the Neumann bands are narrow, about 1 J.l. Schreibersite proper was not observed. The bulk phosphorus content is estimated to be about 0.2%.

Troilite is rather common as 1-10 mm angular nodules and, in these , bluish 0.5-1 mm wide daubreelite bars occur. The sulfides are little damaged and apparently monocrystal­line. Graphite was reported by Guimaraes (1958), and it may be present of course; but the black particles believed by him to be graphite are most probably only defects from polishing.

Patos de Minas is a somewhat weathered hexahedrite which is apparently related to such well known hexahe­drites as Boguslavka and Edmonton (Canada). It should also be compared to Pirapora, another hexahedrite from Minas Gerais, in order to exclude the possibility that Patos and Pirapora are a paired fall. The chance is very small, however, since Patos displays monocrystalline troilite, while Pirapora has shock-melted troilite.

Patos de Minas ( octahedrite ). See Supplement

Paulding County, Georgia, U.S.A.

Approximately 34°N, 84° 50'W

A mass, of which oxidized fragments weighed 725 g, was found about 1901 in Paulding County. It was described as a coarse

octahedrite with 6.34% Ni by Watson (1913). Buddhue (1957: 119) discussed the weathered material. Of this, 161 g is in Chicago.

Peine. See Imilac (in the Supplement)

Perryville, Missouri, U.S.A.

37°44'N, 89°53'W; 180m

Plessitic octahedrite, Opl. Spindle width 60±20 IJ. . Neumann bands. HV 185±9.

Group IIC. 9.58% Ni, 0.54% Co, 0.34% P, 37 ppm Ga, 88 ppm Ge, 11 ppm Jr.

HISTORY

A mass of 17.5 kg was found in 1906 on the farm of Patrick Monaghan, about one mile west of Perryville , in Perry County. The meteorite was about three-fourths buried in the soil and had probably been plowed up previously. In 1912 it was acquired by the U.S. National Museum and was fully described by Merrill (1912) who presented photographs of the exterior and of etched slices· he also presented analyses of schreibersite, separated fro~ the metal (34.1% Ni, 51.1% Fe , 0.30% Co, 14.0% P). The figures and the analyses were reprinted later (Merrill1916a: 127).

COLLECTIONS

Washington ( 12.65 kg main mass and 1.5 kg slices), Harvard (597 g), Moscow (550 g), Tempe (196 g), London (185 g), Chicago (181 g), New York (137 g), Calcutta (98 g), Ottawa (76 g), Bonn (5 g).

DESCRIPTION

The angular mass measured about 21 x 14 x 14 em and weighed 17.5 kg before cutting. It is irregularly covered with terrestrial oxides that form loosely adhering scales, 1-2 mm thick. Regmaglypts, 2-3 em across and rather shallow, occur on several sides; but they are modified considerably by weathering. The fusion crust has disap­peared; however, the heat-affected a: 2 zone is irregularly preserved in many places. It is estimated that, on the average, 1-2 mm of the iron 's surface has been lost by the corrosion. The corrosion penetrates to a depth of 1 or

PERRYVILLE -SELECTED CHEMICAL ANALYSES

percentage ppm References Ni Co p c s Cr Cu Zn Ga Ge Ir Pt

Whitfield in Merrill 1912 9.66 0.55 0.37 150 20 250 + +

Goldberg et al. 1951 9.63 0.68 37 .9 Lovering et al. 1957 0.54 97 285 19 77 Moore et al. 1969 9.81 0.53 0.31 190 25 270 Wasson 1969 9.27 37.0 88.0 11

Perryville is one of the better analyzed plessitic octahedrites.

2 em, selectively attacking the a-phase of the plessite, the grain boundaries and the a-phase of the shock-melted troilite. Locally, a narrow crack extends to a depth of 6 em; this is, of course, also corroded.

Etched sections display a microscopic Widmanstatten pattern of slender kamacite spindles with a width of 60±20 11 and a length which is 10-15 times their widths. The spindles are uniformly oriented on all sections, proving that Perryville originally was a single austenite crystal. In addition to the lamellae, kama cite is also present as irregular grains which appear to be developed as swathing kamacite around primary schreibersite crystals. In this, Perryville resembles Ballinoo , Wiley and several other plessitic octahedrites. The kamacite has Neumann bands and many grain boundaries and subboundaries. Its micro­hardness is 185±9, and, therefore , it is not annealed as Ballinoo. A complete hardness trace perpendicular to the surface is of type II, starting at 195±10 in the a 2 zone, passing through a minimum of 160±5 in the recovered

Figure 1355. Perryville (Moscow). Plessitic octahedrite with numer­ous fine kamacite spindles. Black patches along the surface are due to terrestrial corrosion. Black dots in the interior are shock-melted troilite nodules . Deep-etched. Scale bar 16 mm.

- . d . ·~

.A&41J .,~ Figure 1356. Perryville (U.S.N.M. no. 428). Kamacite spindles and grains almost all with nuclei of schreibersite . Etched. Scale bar 200 IJ. . (Perry 1950: Volume 7.)

Perryville -Persimmon Creek 967

transition zone and leveling off at 185±9 below a depth of about 7 mm.

Taenite and plessite cover 20-60% by area. No comb plessite is present; all fields are finely subdivided in kama cite and taenite, as seen in, e.g., N'Goureyma and Wiley. The cells of the kama cite are 2-20 11 across, and there are numerous taenite blebs of the same general size in the boundaries. Even taenite, as small as 5 11 across, displays a more or less symmetric nickel gradient with a low-nickel interior which is either martensitic or a duplex, poorly resolvable a+ r mixture. The microhardness ranges from 200 to 350, according to the nickel content and microstructure.

Schreibersite is very evenly distributed as 5-50 11 angular, or irregular, crystals that are always enveloped in a 20-40 J1 wide a-rim. Locally, a 400 xSO or 200 x 60 J1

schreibersite crystal may be found; and these appear to have formed along the dodecahedral planes of the parent taenite crystal. Small schreibersi te grains, 1-10 11 across, occur within the plessite fields.

Troilite occurs with a frequency of one per 25 cm2 in form of 0.1-2 mm nodules or 4 x 0.5 mm short lamellae. No troilite nodule larger than 7 x 8 mm was observed on sections totaling 1250 cm2 . The nodules have irregular fringes against the metal because the metal was partly dissolved when the troilite shock-melted. The metal-sulfide mixture solidified rapidly as a fine-grained eutectic of 1-211 grains. Where less metal was incorporated, the sulfide grain size increases to 20 or 50 Jl. Daubreelite must originally have been present on the 5% level, since it now occurs as fine, rounded droplets 1-211 across, well dispersed in the troilite. The schreibersite rims, which were originally present around the nodules, are shattered and partially dispersed in the sulfide melt. A 20011 chromite grain,

located in the midst of the troilite, is brecciated and invaded by melted sulfide veinlets. The short distance that the fragments of schreibersite and chromite have been able to move indicates that the troilite melting was immediately followed by solidification, a fact that is best explained if we interpret the event as a result of shock and relaxation.

Perryville is a plessitic octahedrite which is closely related to Kumerina, Wiley and other group IIC meteorites. Its plessite morphology and its hardness indicate that it is not as well annealed as Ballinoo, which it otherwise resembles.

Specimens in the U.S. National Museum in Washington:

12.65 kg main mass (no. 428, 13 x 13 x 11 em) 1,030 g slice (no. 4 28, 12 x 12 x 0.9 em)

441 g slice (no. 428, 12.5 x 9 x 0.6 em)

Persimmon Creek, North Carolina, U.S.A .

35°3'N, 84°14'W; 800 m

Polycrystalline, silicate-rich, plessitic octahedrite, Opl. Spindle width60±301J..HV 180±10.

968 Persimmon Creek

Group I, Copiapo subgroup. 14.45% Ni, about 0.2% P, 3% S, 35 ppm Ga, 78 ppm Ge, 0.65 ppm Jr.

HISTORY

In the spring of 1893 a mass of about 5 kg was found on the farm of W.W. Young near Persimmon Creek, in the southern part of Cherokee County (Tassin 1904). Accord­ing to letters in the Smithsonian Institution from the agent, Thorn Smith, the locality was on top of a high ridge, only a short distance from Payne Mountain and Hothouse. The corresponding coordinates are given above; they take us about 100 km farther west than the coordinates in Hey (1966). The mass was purchased by the U.S. National Museum and described, with an unsatisfactory analysis, by Tassin ( op. cit.). His photomacrographs of etched slices show the unusual mixture of metallic and nonmetallic parts. Earlier, a fragment of 485 g had been purchased by Julius Bohm, Bonn, and from it several small sections were put in circulation. Cohen (1903c) and Klein (1904b) briefly described some of this material. Merrill (1916a: 127) gave a brief description with a photomacrograph, and Farrington (1915: 348) reviewed the literature. Bunch & Keil (1969) examined the silicates and grouped Persimmon Creek with Copiapo, while Wasson (1970b) showed that the Copiapo group in its trace-element composition was related to the large group I.

COLLECTIONS

Washington (3.5 kg), Chicago (254 g), Budapest (185 g), Canberra (88 g), Bonn (56 g), Strasbourg (44 g), Berlin (22 g), New York (14 g).

DESCRIPTION

The original dimensions were approximately 14 x 10 x 10 em. Since the mass is significantly weathered, it is friable and disintegrates rather easily along the boundaries between metallic and nonmetallic parts. No fusion crust and no heat-affected a2 zone are preserved ; on the contrary, the angular mass is covered with cavernous, 1-5 mm thick, terrestrial oxides in an irregular way, and corrosion pene­trates deep in to the interior.

Etched sections display a messy texture of metal, troilite , graphite and olivine. Some sections may show 90% by area of metal, but on the average the metallic compon­ent constitutes about 75%. The metal was originally a polycrystalline aggregate of austenite grains, each 5-30 mm in diameter. The individual grains are decomposed in a

Widmanstiitten pattern, having formed straight, long (~ ~ 40) kamacite sparks with a width of 60±30 !J. , in a pattern which resembles Butler. The acicular kamacite units do not form a continuous, lamellar grid, and cover only 10-30% by area. The kamacite spindles are subdivided in long cells , and the microhardness is 180±10. The parent austenite grains are separated by grain boundary kamacite that forms 100-20011 wide ribbons, or they are separated by substantial amounts of nonmetallic material. Taenite and plessite cover 70-90% by area of the metallic part. Most plessite fields have a yellow taenite rim, a transition zone of martensite , and an interior of martensite and annealed martensite which has formed fine-grained , duplex a+ 1 structures. The microhardness decreases from about 350 in the rim zone to 250 in the duplex interior. Comb plessite and pearlitic plessite were not observed.

Schreibersite is present as small skeleton crystals, 1 x 0.1 mm in size, and as 50-20011 thick rim zones upon troilite. It is further common as 5-2011 blebs in the more open-meshed plessite. The bulk phosphorus content is estimated to be about 0.2%. The schreibersite is monocrys­talline but brecciated and has a hardness of 900±30.

Troilite is very common and occurs mainly in two forms . Large , rounded monocrystalline nodules of 2-20 mm size constitute , on the average , 15% by area while a minor part is closely associated with the silicates and graphite. The troilite nodules are relatively pure and daubreelite-free but veined by pentlandite from terrestrial exposure. The nod­ules are normally enveloped in a continuous, 100-20011 wide rim of swathing kamacite.

About 10% by area is a heterogeneous mixture of olivine, troilite , graphite, and a little plagioclase and pyroxenes. The well-rounded olivine grains are 25-400 11 across, and they are frequently covered by a 1-10 !J. thick coating of graphite. The intercrystalline concavities are filled with troilite and more graphite. The olivine is locally brecciated and penetrated by 1-511 wide troilite veins.

An unusual cluster of graphite spherules, each 0.2-1 mm across, occurs quite locally in a 2 em metal grain. The spherules are composed of radiating sheaves of graph­ite, and a second generation of unoriented graphite is deposited as a 10-20011 wide rim zone. Winding veins of 10-50 11 wide kamacite subdivide the nodules in much the same way as seen, on a much coarser scale, in certain Canyon Diablo graphite nodules (e.g., Rifle and Mount Elden). The adjacent metal is an equiaxial network of kamacite and taenite, and graphite occurs as 1 11 wide grain

PERSIMMON CREEK - SELECTED CHEMICAL ANALYSES

The analysis was performed on metal with a typical ( 1904) but not identified . It is probably another instance of Widmanstiitten structure. The metal constitutes, on the interpreting chlorine, introduced by terrestrial ground average, 75% of the volume, the remainder being troilite , water, as of cosmic origin. graphite and silicates. Lawrencite was reported by Tassin

percentage Reference Ni Co P c Wasson 1970b 14.45

s Cr Cu ppm Zn Ga Ge lr Pt

34.7 78.3 0.65

boundary fillings. The jagged linear facets of many taenite fields, apparently partly conditioned by graphite veinlets, are also quite unusual. Terrestrial corrosion unfortunately blurs the structure somewhat, since the ferrite easily deteriorates when it is so closely coupled to graphite and taenite.

Persimmon Creek is in many respects an unusual meteorite. On the other hand , the structure clearly indi­cates that it is related to the carbon-containing group I irons. It forms - with Pitts, Soroti , Four Corners and several others - a natural subgroup of high-nickel meteor­ites which are also rich in troilite, graphite, and silicates. The fine kamacitc spindles in a plessitic matrix and the 14.5% Ni place Persimmon Creek in a rather isolated position in the high-nickel end of group I.

Specimens in the U.S. National Museum in Washington:

2,017 g half mass, fragmented (no. 318, 14 x I 0 x 6 em) 929 g fragment , deteriorating (no. 318, 10 x 6 x 5 em) 365 g fragment (no. 318, 7 x 6 x 2.5 em) 200 g rusty fragments and shales (no. 318).

Persimmon Creek - Petropavlovsk 969

Petropavlovsk, Kemerovskoj Oblast, RSFSR

53°21'N, 87° 11'E

Medium-coarse octahedrite, Om/Og. Bandwidth 1.3±0.3 mm. Neu­mann bands. HV 150-180.

Group I judging from the structure. 8.48% Ni, 0.18% P.

The examined sample has been artificially reheated to 500-800° C. It is not clear whether the whole mass has suffered maltreatment.

HISTORY

A mass of 17lh pounds (Russian Funts, each equivalent to 408 g, i.e., 7.2 kg) was discovered in the Petropavlovsk gold mine near the Mrasa River in Siberia in 1840. It was found at a depth of 9.5 m in the lower part of gold-bearing alluvial gravel which was being exploited by the Imperial Kolywany Works. The mass was acquired for the Mining Institute in St. Petersburg (Leningrad) and described in some detail by Erman (1841) . He noted that several other minor fragments had been fo und in the same gravels, but that they had been discarded because they were believed to be broken parts of the gold-washing machinery. Erman

Figure 1357. Persimmon Creek (U.S.N.M. no. 318). The mass consists of polycrystalline taenite with intercrystalline aggregates of troilite, silicate and graphite. Each precursor taenite grain is enveloped in swathing kamacite and independently transformed in a Widmanstiitten pattern. Deep-etched. Scale bar I 0 mm. S.l. neg. 1427.

970 Petropavlovsk

proposed that the masses were not of meteoritic origin, but represented ancient artificial products from the "Schmiede Tataren" (blacksmith Tatars) . However , this view was vigorously opposed by Sokolovskij and Ivanov who had identified 2-7% nickel in the mass (quoted in Erman 1841) . The meteoritic o rigin has been supported by all later authors as , e .g. , Partsch (1843) , Buchner (1863 ; 1867) and Brezina (1885 : 211 ) . Wiilfing (1897) and Hey ( 1966) listed a number of additional references .

The coordinates of the place of discovery have been given very differently by Erman (1841), Brezina (1896 : 358) and Ward (1904a: 20). The improved coordi­nates by Krinov ( 1962: 117) and Hey (1966) are quoted above. The locality is about 19 miles south-southeast of Kuznetsk between the Tom River and the Lake Telezk .

COLLECfiONS

Leningrad (5,935 g main mass and 164 g slice), Vienna (100 g), Moscow (59 g), Chicago ( 45 g) , London (12 g), Paris (11 g), Gottingen (6 g), Calcutta (6 g).

DESCRIPTION

The mass, which measured 18 x 14 x 7 .5 em before cut ting, is an irregular triangular lump which shows rounde d edges and is covered in places with up to 2 mm thick layers of oxide-shales.

The sample examined here is a fragment of 45 g (Chicago Me 1115), originally acquired by H.A. Ward (1904a) by exchange with Leningrad. It measures 45 x 30 x 8 mm and is clearly detached from the main mass by chiseling. It shows ears, ove rfolding and chise l marks , and in one place there is a 3 x 2 cm2 flat hammered area. No fusion crust o r heat-affected a2 zones are preserved.

Figure 1358. Petropavlovsk (Chicago no. IllS). Acicular plessite fie ld and fissured schreibersite along a grain boundary (above left). Etched. Scale bar 100 Jl.

The etched section exhibits a medium-coarse Widman­stiitten structure of straight , somewhat bulky (~ ~ 12) kamacite lamellae with a width of 1.3±0 .2 mm. The kamacite is rich in subboundaries decorated with 0.5-2 }J.

rhabdites . Neumann bands are common. The hardness is very low , 155±5 and , as we shall see below , due to an artificial reheating .

Taenite and plessi te cover 15-20% of the section. Comb plessite is abundant as up to 6 x 2 mm fields , but also the acic ular variety with pointed, 5-20 }J. wide kamacite plate­lets is very common . Pearlite with 0 .5-2 }J. wide taenite lamellae (H ~ 170) occurs locally. Some of the pearlite fie Id s are rich in haxonite which forms isotropic hard areas (H ~ 600), to some degree filling the kamacite part of the pearlite . All taenite is yellowish , or even shows a brown mosaic structure of the type which otherwise is only met with in the heat-affected a2 zone of iron meteorites.

Schreibersite is common as 20-100 }J. wide grain bound­ary precipitates and as 20-100 }J. wide , irregular particles within the open-meshed plessite fields. Rhabdites occur in profusion as 5-15 }J. thick tetragonal prisms and as a smaller generation of 1-3 }J. particles . The phosphides are brecciated and often di splaced I- I 0 }J. by shear. They are now mostly recemented by terrestrial corrosion products .

Troilite , cohenite, graphite and silicates were not detected in the small sample avai lab le, but they will probably be fou nd when larger sections are examine d.

Now, unfortunately, the Chicago sample has been arti­ficially reheated to a peak temperature of about 800° C. Evidence for this is (i) the a2 crystallites which are present at one end, together with chise led fissures following the

Figure 1359. Petropavlovsk (Chicago no. 1115). Pearlitic plessite with cloudy taenite edges. A sheared rhabdite prism below, with in cipient recrystallization in the adjacent kamacite. Etched. Scale bar 30 Jl.

PETROPA VLOVSK - SELECTED CHEMICAL ANALYSES

percentage ppm References Ni Co p c s Cr Cu Zn Ga Ge Ir Pt

Dyakonova & Chari ton ova 1963 8 .48 0.40 0.18 200

. ; . . . ··.

·#·· ·.

'· ...:-

: _· . f\ .. . '· ·· . \ · ~·' ... ~.. .

• ; ' • • I

': .f·>· ·.

' '.'::: ..

.. :~

'· "" :: . .

: •

······:.1:·.

.... ,., . ·, , .

Figure 1360. Petropavlovsk (Chicago no. 1115). Pcarlitic plessite with haxonitc (H) and schreibersite (S). Fine rhabdites and Neu­mann bands in the adjacent kamacite. Etched. Scale bar 30 Jl.

! ·-·-.' .. I _ , 0~· ·_ :_._ ·. , /l \ . "

. ~ .

. .. ·' 0 ·~ 11 ' ... ~ ,

. _';

' ··-~

\ .. ~ -

~, "

0 .\

~ ;

' " ·" '\

:~

it

-. · · \;"

~ - · ~ '

..

t:J ·

~~~

>!

1" .-· \)

a

0

<'& (i

'\;

Figure 1361. Petropavlovsk (Chicago no. 1115). Unequilibrated 0< 2

grains and rhabdite prisms with indistinct reaction halos. A clear taenite lamella to the extreme left. Indications of artificial reheating to about 800° C. Etched. Scale bar 100 Jl.

weakly adherent Widmanstatten grain boundaries ; (ii) the narrow reaction zones around the rhabdites in this same area; the phosphides have not been remelted , but have adjusted their nickel content downwards, thereby creating weird, diffuse border zones about 1 !J. thick between phosphide and kamacite; (iii) the Neumann bands are recrystallized in places , or they are partially dissolved to a broken appearance; (iv) the terrestrial corrosion products are decomposed somewhat to metal and high temperature oxides which form typical laceworks 5-15 !J. wide. Later, additional corrosion has somewhat blurred the picture.

There must have been a temperature gradient across the sample, from about 800° C in the a 2 end to about

Petropavlovsk- Picacho 971

500° C in the opposite end where Neumann bands are preserved. The hardnesses of all phases have been severely influenced by the reheating; most phases have recovered or even recrystallized showing low hardness values, relative to what is normally present in a group I iron (compare, e.g., Toluca). Where the kamacite attained peak temperatures above 800° C it transformed upon cooling to the serrated a 2 phase with characteristic hardness values of 175. The reheating must have been short (less than half an hour) since no large scale diffusion has occurred. The mass was perhaps divided by hot chiseling. It is not known to what extent the main mass itself was reheated.

Petropavlovsk is a normal iron meteorite , transitional between the medium and coarse octahedrites and related to Toluca, Shrewsbury and Bischtiibe. Its trace-element con­centrations will probably indicate that it is a normal member of the resolved chemical group I.

Picacho, New Mexico, U.S.A.

33°12'N, 105°01W

Medium octahedrite, Om. Bandwidth 1.0± 2 mm. E-structure.

Group IliA. 7.08% Ni , about 0.06% P, 19.1 ppm Ga, 33.9 ppm Ge , 19 ppm lr.

HISTORY

A mass of 22 kg was found in 1952 ten miles southeast of Picacho, Lincoln County, at a place corresponding to the coordinates above (Mason 1962a : 238). It is undescribed.

1''''1''''1' '''1''''1''''1'' ''1''''1 ''''1"''1"''1''"1' "'I I II I I"'' Figure 1362. Picacho (Tempe no. 660.1). The only known sample shows Picacho to be a shock-hatched medium octahedrite of group IliA. Deep-etched. Scale in centimeters. (Courtesy C.B. Moore.)

PICACHO - SELECTED CHEMICAL ANALYSES

percentage Reference Ni Co P c s Cr Cu

Scott et al. 1973 7.08

ppm Zn Ga

19.1

Ge

33.9

Ir Pt

19

972 Picacho

COLLECfiONS

Tempe (297 g) . The main mass has been acquired by the American Meteorite Laboratory, Denver , according to price lists circulated in 1973.

DESCRIPTION

A brief examination of a 297 g full slice (Tempe no. 660.1, 7 x 5 x 1.5 em) through the mass showed that Picacho is a somewhat unusual medium octahedrite. The lamellae are straight and long (W ~ 25) and display a width of 1.0±0.2 mm. The kamacite is of the hatched £-variety, suggesting shock intensities above 130 k bar. Taenite and comb and net plessite are common but always in very degenerate forms where the taenite component is almost resorbed. Bundles of narrow o:-lamellae are on the verge of coalescing to wider o:-lamellae .

Schreibersite is almost totally absent; it was only observed as scattered 2-10 J1 blebs, substituting for )'-part-

Figure 1363. Picacho (Tempe no. 660.1). An extremely open­meshed plessite field, subdivided into nine kamacite grains of different orientation. The shock-hatched transformation products appear as usual different from grain to grain. Some terrestrial limonite along grain boundaries. Etched. Scale bar 200 It-

Figure 1364. Picacho (Tempe no. 660.1). Shock-hatched kamacite. Etched. Scale bar 30 IL·

icles in some plessite fields. Microrhabdites, less than 1 J1

across, occur in some kamacite lamellae. The bulk phos­phorus content is estimated to be 0.06±0.02%.

Troilite occurs as bars, e.g., 5 x 1 mm, and blebs , e.g., 0.5 mm across, with well developed parallel daubreelite lamellae. The troilite displays multiple twinning except near interfaces where recrystallization to 20 J1 grains has occurred. Rims of swathing kamacite, 0.5-1.5 mm wide, surround the troilite bodies. Cohenite, graphite and silicates were not noted. No fusion crust and no heat-affected o:2 zones were detected, so the mass must have been exposed to weathering for a long period.

From the structural observations, it appears that Picacho is related to Davis Mountains, Haig, Kenton County, Morito and Livingston (Montana), a conclusion which is supported by the chemical data supplied. by Wasson. According to him, Picacho is an end member of group IliA, with lower nickel and higher iridium contents than any other IliA iron. To this may be added the fact

Figure 1365. Picacho (Tempe no. 660.1). Near-surface section showing terrestrial corrosion products invading along the boundaries of an open-meshed net plessite field. Etched. Scale bar 100 IL·

Figure 1366. Picacho (Tempe no. 660.1). A troilite-daubreelite nodule. The troilite has responded to the shock by recrystallization or - in the narrow lamellae - by multiple twinning. Daubreelite (D) is unaltered. Polished. Crossed polars. Scale bar 20 IL·

that the phosphorus content also appears to be lower than in any other iron of group IliA .

Piedade do Bagre, Minas Gerais, Brazil

18°57'S , 44°59'W

Medium octahedrite , Om. Bandwidth 0.75 ±0.10 mm. Neumann bands. HV 173±8.

Anomalous. 7.50% Ni , 0.39% Co, about 0.07% P, 15 ppm Ga, 26 ppm Ge, 11 ppm lr.

HISTORY

A mass of 59.1 kg was found in 1922 about 16 km southwest of the village of Piedade do Bagre in Minas Gerais. In 1929 the meteorite was acquired by the British Museum where it was described by Spencer & Hey (1930) and a sketch map was given . They presented photographs of the exterior and micrographs of etched slices and discussed, in particular, the Neumann bands which they believed had formed upon impact with the ground. They suggested that the mass was associated with the large fireball observed in the region in 1833 and called Curvello. As discussed below, Pie dade do Bagre is , however , corroded to an extent that probably requires exposure to a terrestrial environment for thousands of years, so Curvello and this meteorite can have no relationship . Hey (1942) used Piedade do Bagre to demonstrate how it is possible to deduce the orientation of an arbitrary section through a meteorite from the Neumann bands .

COLLECTIONS

London (57 kg main mass and 1 ,694 g slices) , Washing­ton (398 g) .

DESCRIPTION

According to Spen cer & Hey (1930) , the irregular lenticular mass weighs 59 kg , and the maximum dimensions in the three directions at right angles are 40 x 32 x 17 em. No regmaglypts are preserved ; the complex and shallow concave surfaces would appear to be the result of terrestrial weathering.

The slice in Washington confirms the weathered char­acter. No fusion crust and no heat-affected a: 2 zone are preserved , and terrestrial limonite covers the surface as rough, 0.1-1 mm thick deposits . Corrosion penetrates at least 5 em in to the interior along the grain boundaries in which 25-20011 wide limonitic veins are common. Since

Picacho - Piedade do Bagre 973

hardness traverses perpendicular to the surface show no gradients whatever , I would estimate that at least 4 mm of the surface has been removed by weathering. Corrosion has furthermore selectively attacked the Neumann bands; a close examination discloses that the reason for this attack is an abundance of 0.5 11 precipitates along both sides of the bands. The chemical potential set up by this segregation has been sufficient to induce local corrosion . It may be compared to the local corrosion along chromium carbides in unstabilized, stainless steels. The state of corrosion is of an extent that I would expect to require thousands of years even in the Brazilian climate. Consequently, it is out of the question that the iron fell in 1833.

Etched sections display a medium Widmanstatten structure with straight, long (W ~ 20) kama cite lamellae with a bandwidth of 0 .75±0.10 mm. This bandwidth is rather rare and would in itself suggest that the meteorite is chemically anomalous. The kamacite has prominent Neu­mann bands. They are significantly decorated along both sides with beads, probably of taenite and phosphide, each less than 0.5 11 across. The Neumann bands have thereby become sensitized, being readily attacked by both labora­tory reagents (Nita!) and natural reagents (ground water). The microhardness of the kamacite is 173±8. Recrystalliza­tion has started along many grain boundaries , but only proceeded to cover a total of less than 0.1 % by area. The recrystallized ferrite forms equiaxial grains, 10-50 !J. across ; and they are usually nucleated at the intersection of a Neumann band with a grain boundary or a schreibersite particle . Concentric growth rings may be distinguished in favorably oriented, new grains . The previous precipitates along the Neumann bands are still faintly visible , but new, sharp Neumann bands are also present - presumably from the deceleration in the atmosphere . Since the precipitation along the Neumann bands and the partial recrystallization of the kamacite require some annealing, it is clear that the Neumann bands antedate the impact with the ground. It appears , in fact , that the majority of Neumann bands in meteorites - and indeed all the prominent ones - date back to a cosmic event related to the release of the meteorite from its parent body.

Taenite and plessite cover about 40% by area , mostly in the form of degenerated comb and net plessite fields. The larger taenite wedges display a transition zone of annealed martensite and a duplex, poorly resolvable interior of a:+ -y . The microhardness ranges from 250 in taenite to 200 in the duplex fields of "black taenite." Many of the comb and net plessite fields display a recrystallized kama­cite matrix with a 20-5011 cellular network .

PIE DADE DO BAGRE - SELECTED CHEMICAL ANALYSES

percentage ppm References Ni Co p c s Cr Cu Zn Ga Ge lr Pt

Spencer & Hey 1930 7.48 0.39 + 2200 97 Scott et al. 1973 7.51 15.1 25 .7 11

974 Piedade do Bagre -Pima County

Schreibersite is almost absent , but may be found as short , 5-10 J.1 wide grain boundary folia . Rhabdites are not observed. The bulk phosphorus content is estimated to be A between 0 .05 and 0.10%.

Troilite is scattered as small nodules and lenticular bodies, ranging from 1 to 5 mm in size. They occur with a frequency of about one per 20 cm2 , and contain 10-20% daubreelite in the form of parallel bars, 0.1-0.5 mm wide.

Spencer & Hey (1930) reported cohenite, but this could not be confirmed.

Piedade do Bagre is a somewhat annealed, medium octahedrite with an anomalously small bandwidth if com­pared to Hen bury, Costilla Peak, Wabar and other irons of similar composition. The trace-element determination indi­cates that it is in some degree related to these irons; Wasson (personal communication) feels, however, that it should be earmarked anomalous, since its combination of Ni, Ga, Ge and lr places it outside the normal IliA range. This conclusion is supported by the bandwidth-Ni combination which is anomalous , too.

Specimen in the U.S. National Museum in Washington:

398 g (no. 1559, 12 x 8.5 x 0.5 em)

Pierceville (iron), Kansas, U.S.A.

37°52'N, 100°40'W

A mass of I 00 kg was found in 1917 near Pierceville , Finney County (Meteoritical Bulletin, No . 8, 1958). About half went to London (Hey 1966: 381), and 22.7 kg is in Tempe. The material, which is extremely weathered, was described by Huss (1965) , who presented three photomacrographs of polished sections.

Among the weathered fragments, samples can be found which still display inconspicuous remains of the meteoritic minerals. I have , on various sections, been able to identify taenite lamellae, comb plessite and rather large schreibersite lamellae, e.g., 5 x 2 and 10 x 1 mm in size. The few structural details suggest that Pierceville originally was a medium octahedrite of group JIIB, related to Chupaderos, Grant and Narraburra.

Pima County, Arizona, U.S.A.

Hexahedrite, H. Shock-recrystallized to about 0.5 mm kamacite grains. HV 175±25.

Group JIA . 5.60% Ni , 0.52% Co, about 0.25% P, 60 ppm Ga, 181 ppm Ge, 8.9 ppm Jr.

Damaged along two sides by oxy-acetylene cutting.

Figure 1367. Pima County (U.S.N.M. no. 1447). The meteorite, originally a hexahedrite , is recrystallized due to shock and the associated reheating. A heat-affected rim zone is present along the edge A-A. Imperfectly polished, black patches are due to corrosion. Deep-etched. Scale bar 10 mm. (Perry 1950: volume 7 .)

HISTORY

A small mass of 210g was in 1947 acquired by S.H. Perry from Professor E.G. Wilson of the University of Arizona in Tucson. Nothing is known of its history , except that it was brought to the university by someone (Bob Heineman?) who was supposed to have found it in the vicinity of Tucson (Pima County) . For years it had been lying unnoticed among other small mineral specimens and sometimes used as a paperweight. The mass was provision­ally described by Henderson & Perry (1949a) , who pre­sen ted photographs of the exterior and of etched slices. The remarkable surface features were interpreted as the result of ablation during flight , but , as discussed below, this cannot be the case. The 210 g mass is only a fragment of a larger , unidentified meteorite. Since it is not certain that the fragment was found in Pima County, or even Arizona, there is no point in attributing coordinates to it. It is unrelated to Navajo and to other Arizona meteorites , a conclusion easily derived from the descriptions given here .

COLLECTIONS

Washington (150 g).

PIMA COUNTY - SELECTED CHEMICAL ANALYSES

Henderson & Perry also reported the composition of the kamacite and of the schreibersite . This was found to be

percentage References Ni Co p c Henderson & Perry

1949a 5.64 0.52 0.10 Wasson 1971 ,

pers. comrn. 5.56

unusually rich in cobalt, containing 2.0%.

ppm s Cr Cu Zn Ga Ge Ir Pt

30

60.3 181 8.9