THE MINERALOGY AND CHEMISTRY OF THE ALTA'AMEEM METEORITE

The Alta'ameem hypersthene chondrite is a light gray brecciated and metamorphosed meteorite composed mainly of olivine (27% Fa), orthopyroxene (24.5% Fs) and plagioclase (An¹⁰). Other minerals include troilite, kamacite, taenite, chromite, ilmenite, clinopyroxene, chalcopyrite, and apatite or merrillite. The mineralogical and chemical analyses suggest that the Alta'ameem meteorite belongs to the amphoterite group of chondrites. The chemical composition includes the following: Fe 3.39, Ni 1.13, Co 0.05, Cu 0.01, FeS 6.48, SiO₂ 39.48, TiO₂ 0.28, Al₂O₃ 2.25, FeO 16.46, MnO 0.40, MgO 25.66, CaO 1.47, Na₂O 1.05, K₂O 0.15, P₂O₅ 0.47, Cr₂O₃ 0.45; total 99.18.     

THE VALDINIZZA METEORITE: MINERALOGY,CHEMISTRY AND MICROTEXTURES

The principal data are collected about the fall and the distribution of the fragments of the Valdinizza, Italy, meteorite. A complete individual, weighing 872 g, preserved in the United States National Museum, Washington, D. C., is described in some detail. The mineralogical composition is olivine, Fa₂₅; hypersthene, Fs₂₃; plagioclase, An₁₀; maskelynite; nickel-iron; troilite; chromite; ilmenite and possibly a phosphate mineral. Valdinizza is a fairly typical hypersthene chondrite, belonging to the type 6 chondrites of Van Schmus and Wood (1967); its structure shows evidence of a period of high-temperature recrystallization; interesting features of shock-metamorphism are notable, the microtexture deformations suggesting a high level of stress     

PIANCALDOLI METEORITE: CHEMISTRY,MINERALOGY AND PETROLOGY

The fall occurred near Piancaldoli, Florence, Italy, at 19.14 U.T. on the 10th August 1968. The fireball broke up in the atmosphere producing a cloud like a balloon. The trajectory and the terminal point were calculated, leading to the recovery of three small meteoritic fragments, found on the roof of a house. Chemical analysis gave the following results: SiO₂ 40.80; TiO₂ 0.15; Al₂O₃ 2. 70; Cr₂O₃ 0.47; FeO 17.20; MnO 0.07; MgO 25.18; CaO 1.95; Na₂O 0.64; K₂O 0.07; P₂O₅ 0.20; NiS 0.93; FeS 6.24; Fe° 2.40; Ni° 0.40; Co 0.05; sum 99.45. In the lithic portion of the meteorite the following minerals were found: both clino and orthopyroxenes (En = 76 to 98%), olivines (Fo = 66 to 98%), troilite, pyrrhotite, pentlandite, kamacite, ilmenite, apatite, merillite, schreibersite, chromite and Henderson phase. From all the mineralogical and petrological data, we conclude that the Piancaldoli meteorite is an “unequilibrated ordinary chondrite,” LL3. The microbrecciated structure of the rock and some shock features were observed, while the rock as a whole is unshocked, suggesting that these features were caused by impact events which took place during the accretion of the parent body.     

THE CHEMISTRY AND MINERALOGY OF THE HOMEWOOD,MANITOBA, METEORITE

The Homewood meteorite is a slightly weathered find of 325 grams discovered in 1970 about 64 km southwest of Winnipeg, Manitoba. It consists of olivine (Fa_25.4; 43.8 normative wt. percent), orthopyroxene (Fs_23.3; 28.5 percent), kamacite and taenite (7.5 percent), troilite (5.6 percent), maskelynite (8.3 percent), chromite (1.0 percent), whitlockite (0.7 percent) and minor patchy Ca pyroxene. Bulk chemical analysis yielded Fe_total 21.60 wt. percent, Fe/SiO₂0.55, SiO₂/MgO 1.53 and Fe^O/Fe_total 0.29. Barred olivine, radiating pyroxene and porphyritic chondrules, all with ill-defined outlines, occur in the meteorite. Most chemical and mineralogical features characterize the Homewood meteorite as an L6 (hypersthene) chondrite. The presence of maskelynite, the undulatory extinction, extensive fracturing and pervasive mosaicism of olivine, and the poor definition of chondrule outlines suggest that the Homewood meteorite has been shocked in the range of 300–350 kbar.     

MINERALOGY,PETROLOGY AND CHEMISTRY OF THE ISNA (C3) METEORITE

A total chemical analysis of the Isna, Egypt, meteorite is similar to analyses for chondrites of type C3, Ornans sub-type; however, comparison with one group of chemical data indicates that Isna is intermediate between the C3(O)'s and C3(V)'s in terms of total Fe. On the basis of atom ratios of Fe, Ca, Al, and Ti to Si, Isna can also be placed into a chemical group which includes types C1 and C2, as well as C3(O). Thin sections show a variety of small, closely-packed chondrules, fragments, and aggregate-like masses in a poorly translucent matrix. Olivine + clinoenstatite inclusions rich in metal and troilite, and olivine-rich inclusions are abundant and show evidence of shock. Ca-Al-Ti-rich inclusions, of probable high-temperature origin, contain olivine, spinel, Ca-rich nepheline, gehlenite, diopside, augite, enstatite, and anorthite. Kamacite and taenite from various occurrences in the meteorite have rather uniform Ni and Co contents, and Ni/Co for kamacite is close to that for several C3(O)'s.     

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.     

THE SAN JUAN CAPISTRANO METEORITE

The San Juan Capistrano chondrite fell on 15 March 1973; the total recovered mass was 56 g. Electron microprobe, chemical and petrographic studies show it to be a member of the H group and of petrologic type 6. Rare gas studies show that only minor radiogenic gas loss has occurred and yield a K-Ar age of 4.6 × 10⁹ years and a Kr-Kr exposure age of 29 × 10⁶ years.     

A NOTE ON THE MINERALOGY AND CLASSIFICATION OF THE VILNA METEORITE

Electron microprobe analyses of olivine, orthopyroxene, clinopyroxene, plagioclase feldspar, chromite, whitlockite, apatite, troilite and metals indicate that the Vilna meteorite is a hypersthene chondrite belonging to the L5 or L6 subgroups.     

SHERGOTTY METEORITE: MINERALOGY,PETROGRAPHY AND MINOR ELEMENTS

The unusual achondrite Shergotty resembles terrestrial diabases, and textural and chemical evidence indicates pre-settling and post-settling crystallization of zoned augite (En₄₈Fs₁₉Wo₃₃-En₂₅Fs₄₇Wo₂₈) and pigeonite (En₆₁Fs₂₆Wo₁₃-En₂₁Fs₆₁Wo₁₈) coupled with late crystallization of plagioclase (Ab₄₃An₅₆/Or₁-Ab₅₆An₄₁Or₃: now shocked to maskelynite), titanomagnetite-ilmenite composite grains, mesostasis (normative Qz₃₄Ab₂₁An₅Or₃₈Fs₂, assuming Fe as ferrous), whitlockite, pyrrhotite (Fe_0.94S), fayalite (Fo₁₀), baddeleyite and chlorapatite. The oxide compositions (Usp₆₂Mt₃₈, Al₂O₃ 2.4, Cr₂O₃ 0.8 wt %; Ilm₉₅Hm₅) indicate ～ 850 °C and log oxygen fugacity ? 14, while the occurrence of fayalite rims on mesostasis next to ilmenite indicates 890 °C. Bearing in mind experimental uncertainties, these data are consistent with late-stage crystallization under relatively high oxygen fugacity, as indicated by coexistence of fayalite, Ti-magnetite and a silica glass. The high alkali content of the maskelynite and mesostasis, coupled with the redox state, indicates that the Shergotty meteorite resembles terrestrial basalts more than any other meteorites. Nevertheless the absence of H₂O, as shown by the occurrence of phosphorus in whitlockite rather than in hydroxylapatite, distinguish the Shergotty achondrite from typical terrestrial diabases. Whereas the FeO/MnO ratios of pyroxenes from the Moon, Earth and several differentiated meteorites are independent of FeO, the ratio for Shergotty pyroxenes changes from 30 to 40 with increasing FeO, and the linear trend extrapolates to 0.2 MnO for zero iron. Hence caution is needed in using FeO/MnO as a planetary indicator. For pyroxenes, Na is almost independent of Fe/Mg while Ti increases and Cr decreases with increasing Fe/Mg. Maskelynite contains 0.5–0.25 wt % K₂O, 0.6 wt % FeO, 0.04 TiO₂, 0.04–0.07 MgO, ～ 0.01 BaO and 0.02–0.03 P₂O₅. A bulk analysis calculated from the mode and compositions of the minerals matches quite well with two bulk chemical analyses but not with a third.     

MINERALOGY AND CHEMISTRY OF THE KYLE,TEXAS, CHONDRITE

The Kyle, Texas, U.S.A., chondrite was identified in 1965. Electron microprobe analyses and microscopic examination show the following mineralogy: olivine (Fa 26.2 mole %), orthopyroxene (Fs 21.0 mole %), clinopyroxene, plagioclase (An 10.3 mole %), chlorapatite, whitlockite, kamacite, taenite, troilite, chromite, and an iron-bearing terrestrial weathering product. Eutectic intergrowths of metaltroilite and a brecciated matrix indicate that the Kyle chondrite was shocked. Recrystallization and shock have obliterated chondrule-matrix boundaries. A chemical analysis of the meteorite shows the following results (in weight %): Fe 0.38, Ni 1.22, Co 0.05, FeS 5.98, SiO₂ 38.41, TiO₂ 0.11, Al₂O₃ 2.13, Cr₂O₃ 0.55, Fe₂O₃ 8.02, FeO 14.83, MnO 0.31, MgO 23.10, CaO 1.60, Na₂O 0.74, K₂O 0.08, P₂O₅ 0.19, H₂O⁺ 1.73, H₂O^? 0.37, C 0.03, Sum 99.83. On the basis of bulk chemistry, composition of olivine and orthopyroxene, and the recrystallized matrix, the Kyle meteorite is classified as an L6 chondrite.     

THE LOOP CHONDRITE: PETROLOGY,MINERAL CHEMISTRY,AND OPAQUE MINERALOGY

The Loop meteorite was found in 1962 in Gaines County, Texas, at a location very close to that where the Ashmore chondrite was found in 1969. The two specimens were assumed to be fragments of the same meteorite. The Loop meteorite is a type L6 chondrite composed of olivine (Fo_75.4Fa_24.6), orthopyroxene (En_77.6Wo_1.5Fs_20.9), clinopyroxene (En_47.5Wo_45.1Fs_7.4), plagioclase (Ab_84.3Or_5.5An_10.2), Fe-Ni metal, troilite, and chromite. Fe-Ni metal is represented by kamacite (5.8-6.4 wt % Ni, 0.88-1.00 wt % Co), taenite (30.0–52.9 wt % Ni, 0.16-0.34 wt % Co), and plessite (16.8–28.5 wt % Ni, 0.38-0.54 wt % Co). Native copper occurs as rare inclusions in Fe-Ni metal. Both chondrules and matrix have similar mineral compositions. The mineral chemistry of the Loop meteorite is quite different from that of the Ashmore, which was classified as an H5 chondrite by Bryan and Kullerud (1975). Therefore, the Ashmore and Loop meteorites are two different chondrites, even though they were recovered from the same geographic location.     

MINERALOGY OF THE BOCAIUVA IRON METEORITE: A PRELIMINARY STUDY

The Bocaiuva iron contains 10 to 15% by volume of silicate inclusions which are surrounded by kamacite (6.5 wt % Ni). The metal shows a Widmanstätten pattern in metal areas devoid of silicates; taenite evolved in plessite fields. The silicate inclusions occur as nodules, and as irregular or chain-like aggregates in which olivine may be rounded or faceted. The magnesian silicates (forsterite, enstatite, diopside) are similar in composition to those of the group IAB irons, whereas the interstitial plagioclase is much more calcic (An 50) than that usually found. Iron sulfide occurs as pyrrhotite and contains 1–2 wt% Cu. Chromite and euhedral magnetite are accessory phases always associated with pyrrhotite. Some patches of pyrrhotite enclose rounded chromite and small plagioclase crystals displaying compositions different from those of the ground mass of the inclusions. Schreibersite shows a compositional variability. This preliminary study underlines the unusual nature of Ms iron and raises several questions concerning the genetic relations between silicates, sulfide and metal, and the thermal history of the whole material.     

PETROGRAPHY AND CHEMISTRY OF THE FAUCETT METEORITE,BUCHANAN COUNTY,MISSOURI

Nine, possibly ten, stones from northwestern Missouri are known as the Faucett meteorite. These stones are finds, but may be fragments of a large fireball seen in the area in 1907. The meteorite is an olivine-bronzite chondrite (H4) containing approximately 31% chondrules and 69% matrix. Modal analysis gives: olivine 43%, orthopyroxene 28.3%, oligoclase 5.9%, glass 1.2%, metallic grains (both nickel-iron and troilite) 19.7%, other minerals and unidentified grains 2.0%. The chemical analysis is typical of modern analyses of H-group chondrites with a total iron value of 26.59 weight percent.     

MINERALOGY,PETROLOGY AND CHEMISTRY OF THE MESSINA (ITALY) CHONDRITE

The meteorite which fell near Messina, Italy, on 16 July 1955 is a typical olivine-hypersthene (L-group) chondrite. Its mineralogical composition is: olivine (Fa24), orthopyroxene (Fs20) with some polysynthetically twinned clynopyroxene, plagioclase (An10) and merrillite. Opaque phases present are: copper, kamacite, taenite, plessite, chalcopyrrhotite, mackinawite, troilite and chromite. The stone contains abundant chondrules. The matrix consists chiefly of broken chondrules with tiny fragments of crystals and rare amorphous material. Chondrules form more than 42% of the meteorite by volume. Some unusual features of the fabric of this meteorite include silicate grains showing deformation; silicates with fusion spots of dark glass containing blebs of metallic iron; iron and troilite with marginal fusion yielding globules and droplets sometimes showing flow structures. The classification of this chondrite is confirmed by bulk chemical analysis.     

THE MAJOR ELEMENT CHEMISTRY OF LIBYAN DESERT GLASS AND THE MINERALOGY OF ITS PRECURSOR

Pieces of high-silica, natural glass (Libyan Desert Glass), found on the desert surface of western Egypt, have been treated as an enigma for 50 years although it is virtually certain they are similar to tektites in being impact-derived products. New major element analyses of four Libyan Desert Glass specimens agree extremely well with the only other recent analysis and demonstrate that the original bulk analyses reported by Spencer (1939) are in error. The five modern analyses define a very tight chemical range for SiO₂ (97.38–98.25 wt %), Al₂O₃ (1.16–2.26 wt %), total Fe (0.15–0.60 wt % as Fe₂O₃) and TiO₂ (0.13–0.19 wt %). Measurable MgO (0.04–0.20 wt %) was found in one specimen. No other elements are present in greater than trace amounts. Microprobe analyses show that Al, Fe and Ti are all positively correlated with one another and are almost ubiquitously distributed throughout the glass. They must also have been so distributed in the LDG precursor material as mechanical mixing and elemental diffusion in the short-lived melt were limited. In contrast, Mg is sharply restricted in occurrence and correlates only with Fe, strongly suggesting a precursor Mg-Fe oxide or silicate mineral present as rare, discrete grains. Aside from rare accessory minerals, the parent material was a sand or sandstone composed of quartz grains coated with a mixture of kaolinite, hematite and anatase. This conclusion is based solely on the elemental distribution in the glass but is buttressed by the occurrence of both sand and sandstone, in southwestern Egypt, with the requisite mineralogy. However, mineralogic identity need not, in general, translate to a chemical match and it is entirely possible that the specific sand or sandstone facies involved in the glass formation no longer exists after 28 million years. Consequently, it may well be that evidence other than chemical comparisons will be needed to identify the presently unknown parent crater.     

MINERALOGY,PETROLOGY AND CHEMISTRY OF LUNAR ROCK 12039

Rock 12039 belongs to the olivine-depleted group of magmatic rocks characterized by normative and modal SiO₂, absence or very low abundance of olivine, and high FeO/(FeO + MgO), Ti/Cr, and CaO/MgO ratios. Clinopyroxenes in this rock show a complex, essentially continuous, compositional zonation from augite cores through ferroaugite to ferrohedenbergite with an abrupt discontinuity at the pyroxferroite contact and, thus, are different from pyroxene in most other Apollo 12 rocks. Two grains contain thin subcalcic pigeonite zones. Texture, presence of very fine (< 1 μm) exsolution lamallae, and pyroxene zoning indicate a relatively rapid cooling history and pronounced in situ chemical fractionation. Rock 12039, on the basis of mineralogy and bulk composition, is the most highly differentiated member of the olivine-depleted basalt group     

PLASMA CHEMISTRY OF METEORITES—I. CLEANSING AND REDUCTION OF THE ODESSA IRON METEORITE

Three small samples of the Odessa, Texas iron meteorite, two surrounded by sandy soil, were introduced into a hydrogen plasma. The soil was effectively cleansed from the iron surfaces, being substantially destroyed with only a fine dust remaining. The appearance of the iron meteorite samples indicated that the terrestrial oxidation was reversed, probably to magnetite, Fe₃O₄, and metallic iron.     

MINERALOGY,PETROGRAPHY AND CHEMISTRY OF THE CHONDRITE,KAMIOMI, SASHIMA-GUN,IBARAKI-KEN,JAPAN

The Kamiomi, Sashima-gun (Iwai-shi), Ibaraki-ken, Japan, chondrite (observed to fall in spring, during the period 1913–6), consists of olivine, orthopyroxene, nickel-iron and troilite with minor amount of plagioclase, clinopyroxene, apatite and chromite. The average molar composition of olivine (Fa₁₉) and orthopyroxene (Fs₁₇) indicates that Kamiomi is a typical olivine bronzite chondrite. From the well-recrystallized texture, the presence of poorly-definable chondrules, homogeneous composition of olivine and absence of glass, this chondrite could be classified in petrologic type 5. The bulk chemical composition, especially, total Fe (27.33%) and metallic Fe (17.00%) as well as Fe_total/SiO₂(0.72), Fe_metal/Fe_total (0–633) and SiO₂/MgO (1.59) support the above conclusion. Coexistence of heavily-shocked olivine grains in the matrix composed of olivines and pyroxenes which suffered from light to moderate shock effect suggest that impacting phenomena, small-scaled but locally strong, occurred on the Kamiomi parent body.     

INTERPLANETARY DUST AND CARBONACEOUS METEORITES: CONSTRAINTS ON POROSITY, MINERALOGY AND CHEMISTRY OF METEORS FROM RUBBLE-PILE PLANETESIMALS

This paper discusses measured textures, porosity, chemical compositions and the minerals of interplanetary dust and meteorites from primitive planetesimals and how this information can be used to explain some of the observed physical and chemical properties of meteor phenomena.