Paul Ramdohr

Chromite and chromite chondrules in meteorites—I

Abstract In a number of chondrites, several chondrules have been found containing chromite as a major component. The second, most common mineral in these chondrules is usually an albite-like plagioclase. Besides coarse grains of chromite, many chondrules contain fine chromite grains, intergrown with feldspar as pseudomorphs after a previously decomposed mineral, probably kosmochlor. Transitions to chromite aggregates, which may represent deformed chondrules, are present. All of the chromite-chondrules, reported on here, are firmly intergrown with the meteorite matrix; feldspar is the binding mineral. Since skeletal crystals of chromite are present in several chondrules, they must have formed at very high temperatures and cooled rapidly. The possibility that “metamorphism” of chondrites caused the welding of many chondrules with the meteorite matrix is also discussed. According to the authors opinion, most properties of “metamorphosed” chondrites can be explained more readily by a high temperature of formation followed by slow cooling.

A calcium-aluminum-rich inclusion from the Essebi (CM2) chondrite: Evidence for captured spinel-hibonite spherules and for an ultra-refractory rimming sequence

Abstract An unusual refractory inclusion was discovered in the Essebi (CM2) chondrite. The inclusion has high concentrations of refractory lithophile and siderophile elements, with strong enrichments of the most refractory elements (Lu, Sc, Hf) in one part of the inclusion. The inclusion consists of a melilite-rich core partially surrounded by a very refractory rim, which in turn is covered by a mantle enriched in Si, Al, Fe, Mn, Cl, and S. Melilite compositions vary from Ak 10–26 in the core to Ak 0–12 in the rim. The core contains several complex framboids consisting of spinel + fassaite or spinel + hibonite. These framboids are probably spherules of the types reported from Murchison, and were possibly captured by the molten inclusion before it solidified. These findings may indicate a genetic link between framboids in CAIs and the spinel-rich spherules in Murchison. The rim sequence consists of the following five layers from inside to outside: 1. (1) hibonite + spinel + melilite; 2. (2) hibonite + perovskite + spinel + melilite (melilite in this layer is altered to sodalite + nepheline + calcite); 3. (3) a hibonite-corundum solid solution; 4. (4) a spinel — corundum solid solution (as much as 0.1 mole fraction Al 2.67 O 4 ); 5. (5) Sc-rich fassaite (as much as 6.2 wt.% Sc 2 O 3 ) + spinel − Al 2 O 3 solid solution + Al-rich diopside. Pt-rich metal crystals occur only in the rim. Some of these metal crystals contain minor amounts of Zr and Hf, indicating that they formed under reducing conditions. The bulk mineral chemistry and texture of the Essebi inclusion indicates a complex history involving capture of solid spinel and spinel — hibonite spherules similar to the Murchison type by a refractory melt droplet, solidification of the droplet without obliteration of the spherule textures, transportation of the composite object to hotter regions of the solar nebula where the very refractory rim condensed, alteration of melilite to sodalite + nepheline + minor calcite, and finally burial in the Essebi parent body. The Cl-, S-bearing mantle probably formed by reactions between the inclusion and liquid and gaseous phases in the parent body.

Opaque Minerals of the Lunar Rocks and Dust from Mare Tranquillitatis

The opaque minerals in the lunar rocks 10047, 10050, 10057, 10059, 10068 and in the dust were studied. Rock 10047 contains ilmenite as a main component besides Al-bearing chromian ulv�spinel, a new Ti, Fe, Zr, Y, Ca silicate, troilite, cobaltian α Fe, minor hafnian baddeleyite and dysanalyte. Dysanalyte contains Ca, Ti, and Fe as major elements and shows concentrations (rare earth elements together ≈ 10 percent) of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Hf, Y, and Zr plus traces of Nb, Ba, and Na. The chemistry of ilmenite in the igneous rocks shows no appreciable variations. A new mineral of the solid solution series MgTi2O5-FeTi2O5 has also been encountered in the polymict breccias. The microbreccias and the fines contain meteorite debris indicating an impact origin.

Die schmelzkruste der meteoriten

The fusion crust of meteorites is modified by many factors (orientation during flight, heat conductivity in the whole meteorite and in the components, chemical reactivity, etc.). In spite of that, some properties can be astonishingly alike, and the zonal arrangement of mineral associations shows many relations nearly everywhere. Of special interest may be the formation of magnetite, wustite and a ‘high temperature maghemite’, the alterations in chromite, ilmenite, iron, alabandite and niningerite, ‘Henderson phase’ and graphite.

The geochemistry of the opaque minerals in Apollo 14 crystalline rocks

Abstract The opaque minerals in rock 14310, a high-alumina fine grained basalt consist of ilmenite, and optically anisotropic chromium ulvospinel, native FeNi metal, baddeleyite, tranquillityite, schreibersite, and a Fe, Ni sulfide (pentlandite or chalcopyrrhotite?). The opaque assemblage of rock 14053, a high-Fe medium grained basalt with subophitic texture consists of ilmenite, a titanium-chromite, chromium ulvospinel, troilite, FeNi metal, fayalite with breakdown products including pure Fe, tridymite and silica glass. In rock 14310 only one spinel was found; it is a chromium ulvospinel which occurs in pyroxene and the groundmass and is similar in composition to the ulvospinels formed during late-stage crystallization of Apollo 12 rocks. Spinels encountered in 14053 are a titanium aluminium rich chromite, chromium ulvospinel and titanium picotite. Their composition is similar to spinels found in the Apollo 12 microgabbro 12018. The Fe Ni metal in 14310 contains 1.5 to 37 wt % Ni and 0.5 to 1.9 wt % Co and occurs middle to late in the paragenetic sequence. These Ni contents cannot be correlated with the mineral assemblage in which the metal phase occurs. Two coexisting iron phosphide minerals,schreibersite, one a Ni-free variety and the other containing 23 wt % Ni, were found in FeNi metal and troilite. This is the first reported occurrence of schreibersite as anindigenous mineral in the lunar rocks and casts suspicion on the criterion for meteoritic contamination used with the Apollo 11 and 12 samples. The zirconium dioxide, baddeleyite, is commonly associated with the opaque minerals, mainly ilmenite. Electron microprobe analyses indicate the presence of minor Zr in both ilmenite and ulvospinel (0.2 up to 0.57 wt % ZrO2 in ilmenite versus 0.03 to 0.19 in ulvospinel). i.e. Zr is preferentially concentrated in the ilmenite structure. The presence of schreibersite in 14310 and the late stage breakdown of fayalite to pure Fe + silica are strong evidences supporting crystallization under extremely low ƒ:02.

Zinc, lead, chlorine and FeOOH-bearing assemblages in the Apollo 16 sample 66095: Origin by impact of a comet or a carbonaceous chondrite?

Abstract Sample 66095, 89 collected from station 6 from the lunar Highlands in the Descartes Site shows evidence of mild to severe shock. These shock features are accompanied by an unusual enrichment in the volatile elements Cl, Zn and Pb and by the presence of FeOOH. FeOOH occurs in two distinct assemblages: (1) with metallic FeNi, (2) with troilite, sphalerite and two Cl bearing Zn, Fe sulfates . Lead is present exclusively in the second assemblage at the boundaries between troilite and goethite. Lead concentrations up to 0.4% were found. However, the nature of lead-bearing phase is unknown. X-ray fluorescence analyses of a 10 × 6 mm area of the thin section also yielded enhanced chlorine, sulfur and zinc contents. The formation of this unique assemblage and the introduction of the material rich in volatile elements is very probably genetically connected with an impact of a carbonaceous chondrite or a comet. The small range of the reaction between the volatile rich gases and metallic FeNi and troilite indicate a short-live-phenomenon and thus fumarolic activity is a very unlikely process.

Lunar pentlandite and sulfidization reactions in microbreccia 14315, 9

Detailed microscopic studies of the Apollo 14 breccia 14315,9 indicate that sulfur and nickel migrations took place. Reactions between mobilized sulfur and metallic NiFe, ilmenite and an Fe-bearing silicate on the one hand, and between migrated Ni and preexisting troilite on the other hand, were observed. Iron, troilite, ilmenite and an iron-bearing silicate (? pyroxene) are affected in decreasing order. Due to the reaction between migrating Ni and troilite pentlandite is formed. This is the first report of pentlandite in lunar samples.

α-Corundum from the lunar dust

Abstract White grains with a bright luster were extracted from a heavy fraction ( D > 4.03g/cm 3 ) of the Apollo 11 fines (sample no. 10084,32). The diameters of these grains range from 40 to 100 μm. They were identified as α-corundum by X-ray diffraction and by electron muprobe analysis. Scanning electron muscopy showed that these grains are composed of innumerable tiny, euhedral α-Al 2 O 3 crystals with their typical habit.

Ein neuartiger Typ „hydrothermaler” Cu-Ni-Lagerstätten

Ores from two claims tested for Cu, Ni, Co and noble metals were examined microscopically and by using the microprobe. The deposits are connected with an enormous fault in ultrabasic rocks in southern Cyprus. The very exceptional association varies in strong alterations over shortest distances. The deposits differ regarding the high and low content of pyrrhotite. Cu-bearing minerals are cubanite and abundant valleriite; Ni-bearing ones pentlandite, mackinawite, oregonite, heazlewoodite; Co is present in two, very probably new arsenides of Co, low in As. — Further are present: Pyrrhotite, chromite, magnetite, graphite, and molybdenite, and as gangue serpentine-minerals and some carbonate. — The deposits give the opportunity to study the rare minerals mackinawite, valleriite, and oregonite together and in relation to pentlandite and chalcopyrite, The mineralisation appears to have occurred during the tectonic movements of the serpentine.ZusammenfassungErze aus zwei Versuchsbauen auf Cu, Ni, Co und Edelmetalle wurden mikroskopisch und mit der Mikrosonde untersucht. Die Schürefe liegen an einer riesigen Bewegungszone im Serpentin in Süd-Cypern. Die höchst ungewöhnliche Paragenese zeigt starke, auf geringste Erstreckung wechselnde Umbildungen. Die Vorkommen selbst sind durch reichlichen bzw. sehr zurücktretenden Anteil an Pyrrhotin verschieden. Träger von Cu ist neben Chalkopyrit Cubanit und sehr reichlich valleriit; von Ni-Pentlandit, Heazlewoodit, Mackinawit, Oregonit; von Co zwei wahrscheinlich neue As-arme Co-Arsenide. Begleiter sind u.a. Pyrrhotin, Chromit, Magnetit, Graphit und Molybdänit, an Gangarten vorwiegend Serpentinmineralien, wenig Carbonate. — Die Lagerstätten geben Gelegenheit, die seltenen Mineralien Mackinawit, Valleriit und Oregonit nebeneinander im Verband und in ihren Beziehungen zu Pentlandit und Chalkopyrit zu untersuchen. Die Mineralisation scheint während der tektonischen Veränderung des Serpentins erfolgt zu sein.

Neue F'ormen meteoritlschen Graphits und mögliche Beziehungen zum Cliftonit

The iron of the Mundrabilla meteorite contains graphite in very exceptional needle-like forms, obviously in many different polytypes. They are similar to graphite in the iron of the Khairpur meteorite. Here the needles || thec-axis form cross-like twins or thrillings with base faces of ∼ 90°. Further growth can fill the interstices to form the cube-like “cliftonite”.