THE CHEMICAL COMPOSITION AND CLASSIFICATION OF THE KAROONDA METEORITE

New bulk compositional results are presented for the Karoonda meteorite which show that it is a member of the Vigarano type carbonaceous chondrites. Use of the petrographic symbol CK for Karoonda is shown to be unnecessary and inadvisable.     

YAMATO METEORITES COLLECTED IN ANTARCTICA IN 1969

The meteoritic community has been tantalized by reports of extensive meteorite finds in Antarctica by members of the Japanese Antarctic Research Expedition. The National Institute of Polar Research has published this introduction and review of the Yamato meteorites collected in Antarctica in 1969. This welcome review reveals that nine meteorite fragments of meteoritic material were found in the region of the Yamato Mountains. Four pieces greater than 60 g in weight have been identified as an enstatite chondrite, a hypersthene achondrite, a type III carbonaceous chondrite and a bronzite chondrite. In 1973 eleven additional suspected meteorites were recovered. Preliminary results show that three bronzite chondrites and one achondrite are among the new finds. In 1974 over 600 pieces of meteorite-like rock have been collected. The volume contains five articles on the original 1969 material. These include a general discussion on their discovery including photographs of the individuals, and notes on the chemical, mineralogical and petrological characteristics of the four large samples. Two articles deal with detailed mineralogic and magnetic properties of these specimens. Information on these interesting finds is welcome. Information on the 1969 and 1974 material is anxiously awaited.     

NAZARETH METEORITES: CLASSIFICATION AND NOMENCLATURE

Six meteorites have been found in Castro County, Texas and named after the town of Nazareth, but each of the four classified specimens has been given two different full names. To clarify this, we have classified the other two specimens and helped to establish approved names for all six specimens. The classes and names of the six specimens, which probably come from six separate falls, are as follows: Nazareth (a), L6; Nazareth (b), L6; Nazareth (c), H5; Nazareth (d), H5; Nazareth (e), H6; Nazareth (iron), IIIA.     

CHEMICAL ANALYSES OF THE MURCHISON AND LOST CITY METEORITES

The abundances of 22 elements have been determined in the recently fallen Murchison and Lost City meteorites. Analyses were performed by 14-MeV neutron activation, thermal neutron activation, and in a few cases by wet chemical techniques. On the basis of these data the composition of the Murchison chondrite is intermediate between previously reported analyses of Type II and Type III carbonaceous chondrites. The data for the Lost City chondrite in general agree well with mean values reported for H-group ordinary chondrites. The low oxygen content of the Lost City chondrite suggests that previously reported oxygen abundances in H-group falls may be too high due to oxidation in storage or weathering prior to collection     

THE CHEMICAL COMPOSITIONS OF THE STONE METEORITES YAMATO (a), (b), (c) and (d), AND NUMAKAÍ

The stone meteorites Yamato (a), (b), (c) and (d) were found in Antarctica in 1969, and the chondrite Numakai was seen to fall in Hokkaido, Japan, in 1925. The chemical compositions of these meteorites have been determined by classical and instrumental methods. With the help of the stepwise fractional dissolution method the chemical composition confirmed the author's previous classification of Yamato (a), (b), (c) and (d) as enstatite chondrite, Ca-poor achondrite, type III carbonaceous chondrite and H-group chondrite, respectively. Numakai is classified as an H-group olivine-bronzite chondrite. The distribution of the major elements in each phase of these chondrites is discussed.     

THE CHEMICAL COMPOSITION OF KAINSAZ AND EFREMOVKA

The type III carbonaceous chondrites Kainsaz and Efremovka have been analysed for eighteen major, minor and trace elements by X-ray fluorescence spectrometry. A comparison of the data on Kainsaz with four other Ornans sub-type carbonaceous chondrites reveals a remarkable degree of constancy of composition. Efremovka, together with Leoville and Coolidge, may be distinguished from the other Vigarano sub-type carbonaceous chondrites by their lower Na and K contents, variable Na/K ratios and relatively low Ca/Al ratios. Some observations are made on the ratio Na/K in various types of stony meteorite; the magnitude of the ratio in the basaltic achondrites appears to be more similar to that in the carbonaceous chondrites than in the ordinary chondrites.     

RECOVERY AND CLASSIFICATION OF THIRTY NEW METEORITES FROM ROOSEVELT COUNTY,NEW MEXICO

We report the discovery and classification of 30 new meteorites found in or close to Roosevelt County, New Mexico, including two H3 chondrites and a ureilite; the others are equilibrated ordinary chondrites. Over 160 meteorites representing at least 100 different falls have been recovered from this region, mostly from wind blowout areas. As in Antarctica, small specimens predominate and irons, achondrites and C and E chondrites are rare. Paired specimens are also very difficult to identify.     

PETROLOGY OF THE YAMATO METEORITES (j), (k), (l), AND (m) FROM ANTARCTICA*

The Yamato (j), (k), (l), and (m) meteorites collected from near the Yamato Mountains in December, 1973, are respectively an H-4 and L-5 chondrite, a howardite, and an L-5 chondrite. Yamato (l), the howardite, is a polymict breccia of diogenite and eucrite clasts. Olivine in the chondrites ranges in composition from Fo₇₅ to Fo₈₀, whereas in the howardite, where it is rare, the composition is about Fo₆₀. Pyroxenes in the chondrites are mostly orthopyroxenes and (En₈₃), while the pyroxenes in the howardite are more complex, comprising orthopyroxene, pigeonite, augite, and rare clinohypersthene (in the order of decreasing abundance), with the range from En₈₀ to En₃₇. They form a definite trend, probably formed by the fractional crystallization of the parental magma of the achondrite, and later subjected to exsolution phenomena during the slow cooling. Plagioclase is high-temperature oligoclase in the chondrites, and anorthite in the howardite. Maskelynitization is sometimes observed. Other shock effects are also observed. Opaque phases consist mostly of nickel-iron, troilite, chromite, and rarely ilmenite. Intergrowth of these minerals are common. The accessory minerals comprise quartz, cristobalite, apatite, spinel, and rare uranium-bearing minerals. The bulk composition and genetic significance are discussed.     

THE COMPOSITION OF IRON METEORITES: A STUDY BY FACTOR ANALYSIS

A factor analysis has been performed on nickel and trace element data for iron meteorites. The technique shows that the present distribution of these elements is the result of three processes. These can be identified from the elements involved:

• 1 Ga, Ge, Sb and Zn (condensation and accretion).
• 2 Ni, Pd, Co and Cu (oxidation and sulphuration).
• 3 Ir, Au, As, Re, Pt, Os, Ru and Cr (an igneous event).

The distribution of Mo, however, is not readily explicable in terms of these processes. Within the groups IAB and IIAB only one process is required for all elements, but in groups IIIAB and IVA the situation for Ga, Ge and Sb is more complex.     

INTEROBJECT STRUCTURE OF UNGROUPED IRON METEORITES AS REVEALED BY ADVANCED CLUSTERING: METHODS AND CHEMICAL FEATURES

Using the MASLOC clustering strategy, 61 ungrouped iron meteorites are probed for physico-chemical clusters. The existing classification of 13 resolved chemical groups is used as an internal coherence reference. Results include tentative establishment of a new group: ID (7 members), with chemical features similar to those of the non-magnetic groups IAB and IIICD. Six additional pairings, all with magmatic chemical signatures, are also recognized.     

THE CHEMICAL COMPOSITION OF THE HAVERÖ METEORITE AND THE GENESIS OF THE UREILITES

The chemical composition of Haverö is presented and compared with the composition of the other five ureilites     

THERMOLUMINESCENCE AND THE TERRESTRIAL AGE OF METEORITES

The use of thermoluminescence (TL) to determine the terrestrial age of meteorites is investigated. It is found that meteorites can be divided into two groups. One group, in which members lose their low temperature TL rather rapidly (the “low retentivity” group), may be dated up to about 100 years after fall, although with little accuracy. The other (the “high” group) is more retentive, and may still be dated several hundred years after fall. A meteorite of unknown date of fall may be assigned to the high or low group by laboratory determination of the rate of decay of the low temperature TL. Weathering coats the grains with limonite and lowers the intensity of the TL. The percentage reduction is constant for various intensities, but the peak height ratio is changed. Therefore, for weathered specimens, a method which examines the decrease in the intensity of a single peak is preferred to one which depends upon peak height ratios: this is made possible by artificially irradiating the meteorites. The following terrestrial ages for finds were obtained: Plainview 225–300 years; Dimmitt 280–330 years; Calliham 350–400 years. Bluff, Etter, Potter, Shields and Wellman (c) proved to be too old to be dated by our methods (≥ 500 years). None of the low group finds available to us proved to be young enough to be dated precisely. Terrestrial ages indicate an extremely low efficiency of recovery (≤ 1%) for meteorites that are not seen to fall. Artificially irradiating the meteorites also revealed the fact that 9 of our 19 meteorites were saturated with respect to thermoluminescence when they entered the atmosphere, and therefore that a technique based on this phenomenon would not be applicable to such specimens to obtain their cosmic ray exposure age.     

METEORITES AND THERMOLUMINESCENCE

The TL techniques that have been developed successfully for archaeological and dosimetric applications cannot be unambiguously applied to meteorites because of the possibility that most or all of the meteorite TL is in dynamic equilibrium — its rate of thermal decay balancing its rate of build-up. In this situation, space irradiation temperature and, thereby, orbital information for the most recent eras (10⁵-10⁶ years), can be determined. In only a few instances (e.g. meteorites with very low exposure ages) will the possibility exist that equilibrium may not have been reached, but even here it has to be shown that the exposure event had removed previously existing TL before normal TL dating techniques can be employed. There is some evidence to suggest that the TL sensitivity builds up with time. This raises the possibility of dating major shock and/or reheating events, if it can be shown that such events destroyed the TL sensitivity.     

THE CHEMICAL COMPOSITION OF MAJOR ELEMENTS AND HEAVY TRACE METALS IN CHONDRITES PARAMBÙ AND MARILIA

The chemical composition of the newly observed fallen chondrites Parambù, 1967, and Marilia, 1971, was determined. Wet chemical methods were used for major elements analyses and the abundances of heavy trace elements from tungsten to uranium were determined by spark source mass spectrometry. The chemical composition confirmed the classification of Marilia as an H-group chondrite by Avanzo et al. (1973): Parambù was classified as an LL-group chondrite.     

INFRARED (JHK) PHOTOMETRY OF METEORITES AND ASTEROIDS

We present JHK colors observed for ten asteroids and synthesized JHK colors for seven meteorite groups, samples of iron and nickel metal, pyroxene, olivine, feldspar, a lunar anorthite and some terrestrial mineral samples. Pronounced differences are apparent between the chondritic and achondritic meteorite classes; the chondritic classes show less subdued trends in J-H color which reflect their metamorphic grade We find small but significant differences between the JHK colors of the predominant C and S classes of asteroids. All JHK colors of asteroids observed here fall within the limited domain defined by the various chondritic and iron-rich meteorites but are strikingly different from those of most achondritic meteorites     

FACTOR ANALYSIS OF ELEMENTAL ABUNDANCES IN CHONDRITIC AND ACHONDRITIC METEORITES

Another explorative study of the use of factor analysis in meteorite geochemistry has been made. Forty-two major and trace elements were sought from analyses of 80 stony meteorites in recent articles. Incomplete data reduced the matrix to 30 elements in 55 stones. Missing data were substituted by mean values in the groups CC, (E+H+L+LL) and ACH (13, 28, 14 individuals, respectively): the effect of these substitutions was tested empirically. R-mode analysis with varimax rotation was carried out on these three sub-sets and on the whole set: interpretation focused on factor loadings and scores. Results on the three sub-sets gave little information of geochemical value, although the largest achondrite factor (lithophile elements) permits discrimination of eucrites, aubrites, diogenites and howardites. Analysis of all 55 meteorites showed the variance to be dominated by 1, a refractory-lithophile(Al, Mg, Ca, Zr, Sc, U, Th, La, Eu, Yb) factor, and 2, a volatile-chalcophile (Zn, Te, Cd, Bi, Tl) factor. Factor (1) scores will discriminate chondrites from achondrites: factor (2) scores delineate the compositional trend CC1, CC2, CC3, (E+H+L+LL) except for enstatite chondrites Indarch, Abee which fall with CC1. Further progress would need metal, sulphide and other mineral percentages for each meteorite.     

THE MINERALOGY OF METEORITES

During the past decade the number of minerals recognized in meteorites has doubled, from about 40 in 1962 to over 80 in 1972. The great expansion in our knowledge can be largely ascribed to the introduction of the electron-beam microprobe as a research tool, enabling the quantitative analysis of microscopic grains in polished sections. While most of these discoveries are of minerals present in minute amounts, their identification has elucidated many aspects of meteorite formation. Of particular interest are five phosphate minerals, three of them unknown in terrestrial rocks; a chromium nitride and a silicon oxynitride; lonsdaleite and chaoite, new polymorphs of carbon; ringwoodite and majorite, the spinel and garnet analogs of olivine and pyroxene respectively; a number of calcium- and aluminum-rich silicates in the Allende meteorite, a Type III carbonaceous chondrite which fell in 1969; and several alkali-rich silicates found as inclusions in iron meteorites. Knowledge of the compositional range of the common minerals olivine, pyroxene, and plagioclase has also been greatly increased by recent researches