LITHIC CLASTS IN THE SUPUHEE CHONDRITE

Supuhee is a shocked and brecciated H6 chondrite containing foreign lithic clasts. Three such clasts were analysed with the electron microprobe in an attempt to locate “mysterite,” a volatile-rich material postulated to be present in Supuhee. Clast 1 bears chemical and mineralogical similarities to C1 and C2 chondrites, but its total volatile content, <9.4%, is lower than that of either of these types. The composition of Clast 2 suggests its derivation from H-group chondrite material via loss of metal and sulfide. The third clast is apparently a unique meteorite type bearing compositional similarities to both ordinary and enstatite chondrites. The occurrence of these clasts in a highly recrystallized host is evidence for their incorporation after metamorphism. The presence of Clast 1, coupled with this time sequence, indicates that conditions were favorable for the formation, incorporation and preservation of volatile-rich materials such as mysterite     

COPPER-NICKEL ALLOY IN THE BLANSKO CHONDRITE

Both Fe and Ni were measured in microprobe analyses of a large copper metal rim that formed by exsolution from a large troilite grain contained within an iron-nickel metal grain in the H-group chondrite, Blansko. The Fe content of the copper can be accounted for largely by secondary fluorescence by Cu-K_α of Fe radiation from the adjacent metal, however, fluorescence by Cu-K_β of Ni radiation cannot significantly account for the observed Ni content. Therefore, the copper actually alloys up to 2% Ni, with a concentration gradient dropping to 0.7% away from the copper-metal interface.     

NOBLE GASES IN THE UNIQUE CHONDRITE,KAKANGARI

The Kakangari chondrite has a cosmic-ray exposure age of 5.4 m.y. and a K-Ar age near 4 g.y. Its high cosmogenic ³He/²¹Ne ratio of 7.5 indicates a small preatmospheric mass. The He and Ne are largely of solar-wind origin, presumably implanted during exposure in the regolith of its parent body. The heavy gases Ar, Kr, Xe are largely of planetary origin. Taken together, the low ¹²⁹Xe/¹³²Xe (1.07), low ³⁶Ar/¹³²Xe (225), and high ¹³²Xe content (45 × 10^?10 cc STP/g) are more similar to the values for unequilibrated ordinary chondrites or even C1, C2 chondrites than to enstatite chondrites, and suggest that Kakangari has the same gas-bearing mineral assemblage as the former, in spite of its high degree of reduction (Fa_4.9).     

A REFRACTORY GLASS CHONDRULE IN THE VIGARANO CHONDRITE

Vigarano, a type 3 carbonaceous chondrite, contains a chondrule composed of highly refractory Ca and Al rich glass with minor spinel. The chondrule formed from material similar to the Ca, Al, Ti-rich aggregates that are common in Vigarano and other type 3 chondrites and formation of these refractory aggregates must predate formation of some Vigarano chondrules. Experiments with synthetic analogues and a comparison with studies in the system CaO-MgO-Al₂O₃-SiO₂ indicate a temperature for formation of the chondrule at or above 1700 °C followed by very rapid cooling.     

THE SEONI CHONDRITE

The Seoni (India) chondrite is an H6 group ordinary chondrite that contains olivine (Fa, 19.7 mole%), orthopyroxene (Fs, 15.9 mole%), clinopyroxene, plagioclase (An, 10.3; Or, 5.6 mole%), together with chromite, troilite, kamacite, taenite, chlorapatite, and whitlockite. Recrystallization has been quite extensive as indicated by the presence of few remnant chondrules, low abundance of clinopyroxene and relatively high abundance of well formed plagioclase. Treatment of Fe²⁺ and Mg partitioning between clinopyroxene and orthopyroxene and between olivine and chromite indicates equilibration temperatures of between 875–920 °C.     

THE TAMBAKWATU CHONDRITE

According to its petrography, uniform olivine, Fa_23.8, and pyroxene, Fs_20.4, a total iron content of 22.9 wt % Fe, 16.4 wt % FeO and an FeO/FeO + MgO ratio of 24.7 mol %, the Tambakwatu is a veined, intermediate hypersthene (Cia) or L6 chondrite.     

ROEDDERITE IN THE QINGZHEN (EH3) CHONDRITE

The rare mineral roedderite, (Na_1.09 K_0.89 Ca_0.02)_2.00 (Mg_4.71 Fe_0.27)_4.98 (Si_11.80 Al_0.09)_11.89 O₃₀ has been found in accessory amounts in the highly unequilibrated enstatite chondrite, Qingzhen. It occurs in association with minor amounts of albite and SiO₂ as inclusions within the metal or sulfide phases of metal-sulfide assemblages. The roedderite crystals are connected through oxide and silicate veins to the surrounding matrix. The presence of glass coated vesicles on the surface of the assemblages strongly suggests that roedderite originated in the presence of a fluid phase, presumably during post-accretional planetary processes.     

THE PARSA ENSTATITE CHONDRITE

Two meteoritic stones weighing roughly 600 and 200 g fell on 14 April 1942 near Parsa, Bihar, India. The meteorite is a high-Fe (EH) enstatite chondrite on the basis of its large abundance of chondrules, its low concentrations of refractory elements, the Si content of its metal (25–30 mg/g), and its enstatite composition Mg_0.975Ca_0.007Fe_0.018. The high contents of Zn, Cd and In suggest that Parsa is petrologic type 4. A unique feature is an irregular nodule of coarse enstatite, several cm long which is chemically different in its Ca and Fe content compared to the matrix. We have increased the elemental concentrations by 10% to allow for terrestrial oxidation and hydration. The revised siderophile and moderately volatile element concentrations fall within the range observed in EH chondrites and mostly outside the range found in EL chondrites. Terrestrial alteration is indicated by the presence of limonite and other hydrated minerals as well as the morphologies revealed by scanning electron microscopy. The ²⁶Al activity is 51 ± 6 dpm/kg consistent with the calculated production rate. Cosmogenic track densities combined with the ²¹Ne, ³⁸Ar exposure age of 17 Myr indicate 4–10 cm ablation loss, or a preatmospheric mass of about 40 kg.     

MINOR ELEMENTS IN MARJALAHTI OLIVINE

Precise microprobe determinations of minor elements in olivine from Marjalahti show averages of 0.067% CaO; 0.0211% Cr₂O₃; less than 0.0045% TiO₂; 0.288% MnO; and 30 ppm Ni. The calcium is as high as in some terrestrial plutonic olivines (e.g. Stillwater) but lower than in terrestrial nodule (high-temperature mantle?) olivines, consistent with very slow cooling to low temperatures. The chromium is discrepant with some earlier determinations, and possibly chromium is zoned in most pallasitic olivines. The Ti, Mn, and Ni data are consistent with previous determinations.     

THE COLONY METEORITE AND VARIATIONS IN CO3 CHONDRITE PROPERTIES

The Colony meteorite is an accretionary breccia containing several millimeter-to centimeter-size chondritic clasts embedded in a chondritic host. Colony is one of the least equilibrated CO3 chondrites; it has an unrecrystallized texture and contains compositionally heterogeneous olivine and low-Ca pyroxene, kamacite with low Ni and Co and high Cr, amoeboid inclusions with low FeO and MnO, a fine-grained silicate matrix with very high FeO, and numerous small chondrules with clear pink glass. However, Colony differs from normal CO chondrites in several respects: Although Al, Sc, V, Cr, Ir, Fe, Au and Ga abundances are consistent with a CO chondrite classification, certain lithophiles (Mg and Mn), siderophiles (Ni and Co) and chalcophiles (Se and Zn) are depleted by factors of 10–40%. The shape of Colony's thermoluminescence (TL) glow curve is similar to that of Allan Hills A77307 (another unequilibrated chondrite with CO3 petrological characteristics) and different from those of normal CO chondrites. [ALHA77307 also resembles Colony in having low Mg, Mn, Ni and Co, compared to normal CO chondrites, but it possesses CO-CV levels of Se and Zn and nearly CV levels of Cd.] Colony is badly weathered; it contains 22.7 wt.% Fe₂O₃ and 5.7 wt.% H₂O. Recalculating the analysis on an H₂O-free basis with all Fe₂O₃, NiO and CoO converted to metal, yields an inferred original metallic Fe, Ni abundance of ～ 19 wt.%. This is similar to that of Kainsaz (an unweathered CO3 fall), but much higher than that of all other CO3 chondrites (< 6.3 wt.%). Although it is possible that Colony and either ALHA77307 or Kainsaz constitute distinct CO3 chemical subgroups, the weathered nature of Colony and ALHA77307 preclude the drawing of firm conclusions. Nevertheless, it is clear that CO3 chondrites vary more in compositional and petrological properties than was previously recognized.     

THE CLASSIFICATION OF THE BENARES CHONDRITE

The Benares meteorite is an LL4 chondrite, not LL6 as recorded in the literature. Some specimens labelled Benares are misidentified.     

THE ATLANTA ENSTATITE CHONDRITE BRECCIA

Atlanta is the fifth known brecciated enstatite chondrite. It contains a centimeter-sized troilite-rich clast, similar to those that occur in Blithfield. All of these clasts probably formed in the solar nebula under high pS₂/pO₂ conditions in a gas of non-cosmic composition. The absence of ordinary or carbonaceous chondrite clasts in any of the enstatite chondrite breccias and absence of enstatite chondrite clasts or materials formed at high pS₂/pO₂ ratios in ordinary and carbonaceous chondrite breccias support the model that enstatite chondrites were formed at a location distant from those of the other chondritic groups.     

LITHOPHILE ELEMENTS IN INDIVIDUAL CHONDRULES OF THE H-4 MAFRA CHONDRITE

Bulk and trace lithophilic elements (Al, Ca, Fe, Mn, Ti, Cr, Sr, V and Zn) have been determined in individual chondrules and in other constituents of the H-4 Mafra chondrite by means of flameless A.A. microanalysis. Twenty-four large sized (> 1 mg) chondrules, composite samples of minor-sized (0.1 and 0.2 mg) chondrules and fine-grained “interchondrular” material have been examined. Data on the large-sized chondrules exhibit large compositional variations among cosmochemically coherent groups of elements. A weak anti-correlation was found between the geochemically coherent refractory V and volatile Zn. A possible mass-composition relationship is suggested by the apparent concentration of lithophile high-temperature condensing elements (Ca, Al, Ti) in the minor-sized chondrules. Compositional features tend to support the hypothesis that chondrules originate from a large number of precursor components constituting a distinct grain population in the solar nebula. Melting through a sudden heating of random mixtures of these precursor grains was possibly followed by further condensation of volatiles and accretion.     

NEPHELINE AND SODALITE IN A BARRED OLIVINE CHONDRULE FROM THE ALLENDE METEORITE

Nepheline and sodalite have been found in association with glass in a barred olivine chondrule from the Allende C3V meteorite. The major minerals of the chondrule are olivine (Fo_80–88), bronzite (En₈₅Fs₁₂Wo₃), and chromite. Olivine bars are separated by glass of nearly pure plagioclase composition (An_81–99). Olivine composition is more Fe-rich than predicted by olivine-liquid equilibria (Fo₉₆). Conditions of non-equilibrium are implied from this and the presence of plagioclase glass and small amounts of subcalcic diopside (En₇₅Fs₁₂Wo₁₃) in the chondrule. The properties of this chondrule are consistent with liquid condensation, but melting of an amoeboid olivine aggregate or similar object could also have generated the chondrule-forming liquid. Nepheline and sodalite appear to have crystallized from this liquid under non-equilibrium conditions.     

RARE EARTH AND OTHER ELEMENTS IN COMPONENTS OF THE ABEE ENSTATITE CHONDRITE

Abee clast samples, a matrix sample, a dark inclusion, magnetic and nonmagnetic samples, and bulk samples were analyzed by neutron activation analysis (NAA). The REE were determined by radiochemical NAA. Na, K, Sc, Cr, Mn, Fe, Co, Ni, Zn, As, Se, Sm, Ir, Au were determined by instrumental NAA. High abundances of As, Ir, and Au in the magnetic separate and the correlation of their abundances with the metal content of the clasts indicate that As, Ir, and Au chiefly occur in the metal. Correlations for Zn and Sc indicate that they chiefly occur in niningerite, but a significant amount of Sc may also occur in oldhamite. The dark inclusions do not follow the As and Zn correlations, suggesting that the dark inclusions and clasts are not equilibrated with each other. Correlation of the REE and oldhamite abundances for both the clasts and dark inclusions indicates that the REE chiefly occur in oldhamite. In view of the INAA and mineralogical evidence for non-equilibration among the clasts and a dark inclusion (Sears et al., 1981), the similar REE patterns for clasts (3,3) and dark inclusion (5,1), and the similar mineral composition of oldhamite in clast (3,3) and dark inclusion (5,1), suggest that the oldhamite in the clasts and dark inclusions is of a common origin, which Sears et al. (1981) showed could be formed by condensation. A Tb anomaly of a factor of 2 was found in sample (2,9 and 9,2), and a La anomaly of a factor of 2 was found in clast (3,3). The only other REE anomaly in Abee, a factor of 3.5 for Yb, was found by Nakamura and Masuda(1973). In view of the evidence for equilibration among the clasts, this anomaly must have been introduced shortly before the brecciation process and indicates that no significant reheating has occurred. This concurs with the findings of Sugiura and Strangeway (1981) and Bogard et al. (1982).     

THE GALATIA,KANSAS, CHONDRITE

The Galatia meteorite was found in August, 1971, approximately 7 km ENE of Galatia, Barton County, Kansas (98° 53′W., 38° 39.5′N). The single stone weighed 23.9 kg and is partially weathered. Olivine (Fa_24.9) and pyroxene (Fs_20.9) compositions indicate L-group classification, and textural observations indicate that the stone is of petrologic type 6. Galatia is similar in many respects to the Otis L6 chondrite (found 20 km to the west), but it does not have the brecciated structure of Otis and, thus, it is not part of the same fall.     

EXPERIMENTAL VAPORIZATION OF THE HOLBROOK CHONDRITE

Knudsen cell-quadrupole mass spectrometry has been used to quantitatively determine the composition of the vapor phase produced by heating samples of the Holbrook chondrite to 1300 °C. Maximum observed vapor pressures (atm) of metals are 10^{?5.3 ± 0.3} Na, 10^{?5.8 ± 0.3} K, 10^{?5.3 ± 0.3} Fe, and 10^{?6.6 ± 0.3} Ni at 1200 °C. S₂ (with minor SO₂), H₂O, and CO₂ were also observed in the high-temperature gas phase. Release of intrinsically derived volatiles produced abundant vesicles in the heated sample residues. Some possible implications for chondrite evolution are briefly discussed     

COSMOGENIC RADIONUCLIDES AND NOBLE GASES IN THE WETHERSFIELD (1982) CHONDRITE

The Wethersfield (1982) chondrite was assayed for a suite of cosmogenic radionuclides shortly after fall. Data are reported for ⁷Be, ²²Na, ²⁶Al, ⁴⁶Sc, ⁴⁸V, ⁵¹Cr, ⁵⁴Mn, ⁵⁶Co, ⁵⁷Co, and ⁶⁰Co. A comparison is made with predicted results based on a scaling to the Deep River Neutron Monitor. Noble gases were also assayed in a sub-sample. The cosmic ray exposure age is estimated to be 45 million years.     

THE MADIUN,INDONESIA, CHONDRITE

Madiun is a white, veined olivine-hypersthene, L6 chondrite. It can be classed as such on the basis of its petrography and chemistry, uniform olivine (Fa_24.2) and pyroxene (Fs_21,2) end total iron content of 23.7 wt % Fe.