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 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.     

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.     

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.     

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     

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     

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.     

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.     

THE ELLA ISLAND,GREENLAND, CHONDRITE

The Ella Island, Greenland, meteorite was found in August of 1971. Electron microprobe study of the meteorite revealed it to contain olivine, low-calcium pyroxene, high-calcium pyroxene, plagioclase, kamacite, taenite, chromian-hercynite and troilite. On the basis of fayalite and ferrosilite content, poorly-defined chondrules, absence of glass in chondrules, presence of well-developed feldspar in the matrix and chondrules, and degree of recrystallization of the matrix, the Ella Island meteorite is classified as an L-6 chondrite.     

MINERALOGY AND CHEMISTRY OF THE ASHMORE CHONDRITE

The Ashmore olivine-bronzite chondrite is a group H, type 5 stone which differs from other H5 chondrites mainly in its higher proportion of chromite (0.9 wt %) and in the relatively lower iron and higher magnesium content of the chromite. The modal proportions of opaque phases were obtained by point-counting in reflected light, and the modal proportions of nonopaque silicate phases in the matrix were estimated from traverses of a selected small area by electron microprobe. The consistency between the bulk chemical analysis and the chemical composition calculated from the modal mineral proportions implies that the bulk silicate composition of the chondrules is very similar to that of the silicate matrix and suggests a common source for both chondrules and matrix.     

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.     

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).     

MINERALOGY AND PETROLOGY OF THE YILMIA ENSTATITE CHONDRITE

Yilmia, a new enstatite chondrite contains moderately well defined radiating and granular chondrules. The plagioclase to enstatite ratio is appreciably higher within than outside of the two granular chondrules in our microprobe sections. Osbornite was observed within the granular chondrules, but not in the rayed chondrules or surrounding matrix Major phases include enstatite, plagioclase (Ab₈₀ An₁₆ Or₄), silica, silicon-rich kamacite and titanian troilite. Minor phases are many and varied: sinoite, silicon-rich taenite, schreibersite, graphite, osbornite, oldhamite, “normal” and zincian daubreelite, ferroan alabandite and a new FeZnMn monosulfide The new mineral (Fe_.538 Zn_.246 Mn_.159 Mg_.004 S) closely resembles albandite and could easily have been overlooked in other meteorites unless a microprobe was used. A new form of oldhamite was also found. Indarch oldhamite, analyzed for comparative purposes, consists of two similar but distinct species: Ca_.96 Mn_.005 Mg_.04 Fe_.01 S and Ca_1.000 Mn_.004 Mg_.02 Fe_.005 S. These have not been reported from other meteorites Based on its mineralogy and texture this is a type II (E6) enstatite chondrite that is transitional toward the intermediate type (E5). It is unique in its mineralogical complexity, abundance of taenite, diversity of zincian minerals and monosulfides, and restriction of osbornite to certain chondrules     

A DETAILED CHEMICAL STUDY ON THE BARWISE CHONDRITE

Six fragments of the Barwise meteorite were analyzed for REE and eleven other elements (Al, Ca, Mg, Mn, Na, K, Cr, Fe, Co, Ni and Ba). In addition, two fragments were analyzed for Si and Mg. The chondrite-normalized REE patterns of six fragments studied show interesting systematic variations. Three fragments with relatively high La abundances show a negative Ce anomaly. Since the meteorite in question is a find, it could be suspected that the observed REE fractionations are due to terrestrial contamination. To examine this point, a soil sample from the find site was also analyzed for REE and major chemical elements. It is considered that several facts, especially, the relationships between La and SiO₂ and between SiO₂ and MgO, suggest the pre-terrestrial fractionation rather than the terrestrial contamination. Unexpectedly, it is shown that the REE fractionation observed in the investigated fragments correlates with the metal-silicate and the Fe-Co-Ni fractionations. In this connection, large metal grains were investigated for Fe, Co and Ni contents. A suggestion is presented that this chondrite was formed through the melting of the surface of a planetesimal and the subsequent collision, although the possibility of terrestrial contamination might not be ruled out.     

OLIVINE MICROPORPHYRY IN THE ST. MESMIN CHONDRITE

Olivine microporphyry, of metal- and troilite-poor LL-group composition and composed chiefly of olivine (58 vol. %), pyroxenes (18%, including orthopyroxene, pigeonite, and subcalcic augite), and quartz-oligoclase glass (22%), occurs in and locally intrudes clasts in the St. Mesmin chondrite (LL-group breccia). Its crystallization history resembles that of many Apollo 12 lunar basalts, modified somewhat by a lower bulk Fe/Mg ratio and a higher (Fe+Mg)/Ca ratio. The microporphyry crystallized from a melt which was emplaced during a period of brecciation or between two episodes of brecciation, but after the thermal metamorphism recorded in other components of the breccia. This melt originated by complete melting of normal LL-group material with loss of Fe, Ni, and S, or, less likely, by fusion of such material (LL-7?) which had lost these elements during prior anatexis. Comparison of the St. Mesmin microporphyry with similar material in the Parnallee chondrite (Binns, 1968) suggests that the latter was derived from a different parent, perhaps of C-1 chondritic composition.     

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 TIMMERSOI†, NIGER,HYPERSTHENE CHONDRITE

The Timmersoi meteorite, a new type L5 hypersthene chondrite from the Niger Republic is described and microprobe analyses of its olivine, orthopyroxene, clinopyroxene, plagioclase, kamacite, taenite, troilite, chromite, whitlockite, chlorapatite and limonite presented. Veins and patches of black “glassy” material are regarded as products of shock melting. In places this material contains immiscible droplets of troilite each with one or more well-formed crystals of taenite. Calculations indicate equilibrium between olivine and orthopyroxene with a temperature of equilibration of about 850 °C.