Louis H. Fuchs

Calcium-aluminum-rich inclusions in the Allende meteorite - Evidence for a liquid origin

Abstract We have made a detailed examination of the mineralogy, textures and assemblages of six calcium-aluminum-rich inclusions (CAI) in the Allende meteorite. They can be classified into four types—hibonite-bearing, fassaite- and olivine-bearing, feldspathoid-bearing and fassaite-bearing CAI that are hibonite and olivine free. Examples of each type appear to have crystallized from a liquid rather than by agglomeration of solid nebular condensates. Some lines of evidence for a liquid origin are (1) the presence of spherical and ovoid shapes, (2) rims containing minerals (e.g. hibonite, perovskite) that are more refractory than minerals inside the inclusion, (3) eutectic and poikilitic textures, (4) minerals that are completely enclosed by more refractory minerals and (5) glass and fine-grained grossular stringers. Thermodynamic calculations and comparisons with liquidus phase diagrams indicate that the CAI could have been produced by direct condensation to metastable subcooled liquids that subsequently crystallized ( blander and Katz , 1967) or by remelting of an equilibrium high-temperature condensate by impact. The diopside rims in some hibonite-bearing CAI and the paucity of metal in fassaite-olivinebearing CAI are more consistent with direct condensation of a liquid. The sluggishness of solid-solid reactions at the relatively high temperatures at which the CAI formed argues against assuming equilibrium in calculations at lower temperatures.

Djerfisherite, Alkali Copper-Iron Sulfide: A New Mineral from Enstatite Chondrites

A new mineral, essentially a potassium-copper-iron sulfide, occurs in accessory amounts in the enstatite chondrites Kota Kota (a find) and St. Marks (a fall), and has been identified visually in the enstatite achondrite Pena Blanca Springs (a fall). The x-ray diffraction pattern, electron-microprobe analysis, and its appearance in polished sections all serve to identify it.

Hibonite, Ca2/Al, Ti/24O38, from the Leoville and Allende chondritic meteorites.

Abstract Hibonite [Ca 2 (Al, Ti) 24 O 38 ] was discovered in light-colored, Ca Al Ti-rich and Si Fe-poor, achondritic inclusions of the Leoville and Allende HL-group chondrites. Two varieties of hibonite occur: One emits a bright red-orange luminescence under electron bombardment and has high amounts of Al 2 O 3 (87.7; 87.9) and low amounts of MgO (0.65; 0.8) and TiO 2 (0.68; 0.8). The other emits a bright blue luminescence and is low in Al 2 O 3 (78.7; 79.2) and high in MgO (3.3; 3.7) and TiO 2 (6.5; 7.9) (in wt. %). The oxide CaO is about the same in both varieties. It is suggested that the change in the color of the visible luminescence results from changes in composition. The origin of hibonite which occurs in complex mineral assemblages together with anorthite, gelhenite, wollastonite, aluminous diopside, andradite, Ca-pyroxene, perovskite, spinel, taenite, chromite, and pentlandite, and in close proximity to nodules containing calcite, whewellite, forsterite and many of the aforementioned phases, is discussed. The proposition that hibonite and associated phases originated by contact metamorphism and metasomatism of calcite-dolomite bearing assemblages cannot, at this time, be completely ruled out.

Solar Neutrinos: Proposal for a New Test

The predicted flux on the earth of solar neutrinos has eluded detection, confounding current ideas of solar energy production by nuclear fusion. The dominant low-energy component of that flux can be detected by mass-spectrometric assay of the induced tiny concentration of 1.6 x 107 year lead-205 in old thallium minerals. Comments are solicited from those in all relevant disciplines.

The Phosphate Mineralogy of Meteorites

Nine phosphate minerals are found in meteorites: whitlockite, Ca3(PO4)2; chlorapatite, Ca5(PO4)3Cl; hydroxyapatite, Ca5(PO4)3OH; sarcopside, (Fe, Mn)3(PO4)2; graftonite, (Fe, Mn)3 (PO4)2; farringtonite, Mg3(PO4)2; stanfieldite, Ca4(Mg, Fe)5(PO4)6; brianite, Na2MgCa(PO4)2; and panethite, Na2Mg2(PO4)2. The last four have been found only in meteorites.

Primordial refractory metal particles in the Allende meteorite

Abstract Refractory metal particles containing Os, Re, W, Mo, Ir, and Ru were observed in a Ca-Al-rich inclusion in the Allende meteorite. These particles are the closest to unaltered primordial metal condensates from a nebula yet reported, and appear to have been isolated from the nebula before the condensation of refractories was complete. Computer calculations of condensation indicate that the temperature of isolation appears to be close to the calculated temperature of first formation of oxides (~ 1620 K at 10 −4 atm) indicating that isolation may have been effected by coating of the particles by oxides.

On the occurrence of brianite and panethite, two new phosphate minerals from the Dayton meteorite☆

Abstract Two new phosphate minerals, brianite Na 2 CaMg(PO 4 ) 2 , and panethite (Na, Ca) 2 (Mg, Fe) 2 (PO 4 ) 2 have been found in phosphate-silicate nodules in the Dayton very fine octahedrite. Chemical, optical and physical data are presented for these minerals, and some of the implications of their presence are discussed.

The state of oxidation of some iron meteorites

Abstract Two iron meteorites are now known to contain chlorapatite-silicate-schreibersite assemblages. Thus, phosphorus is present in two oxidation states. Electron microprobe analytical results on the minerals present in these occurrences are combined with thermochemical data in order to examine the oxidation-reduction conditions implied by this assemblage. The silicate phases (olivine, orthopyroxene, clinopyroxene) were found to be out of equilibrium, however, it is still possible to estimate the oxidation state of these meteorites and make direct comparisons with eight other irons and pallasites which contain other phosphate minerals, calcium-free sarcopside and farringtonite, as well as ordinary equilibrated chondrite meteorites. All these metallic meteorites represent approximately the same degree of oxidation as the ordinary chondrites. Some implications regarding the size of a zoned parent body are discussed.

Composition of metal in type III carbonaceous chondrites and its relevance to the source-assignment of lunar metal.

Abstract The metal in seven Type III carbonaceous chondrites has been measured for concentrations of Ni, Co and Cr. Cobalt in kamacite is 3.2 to 5.5 times greater than in taenite on composite grains containing both phases. No correlation was found between the metal compositions and sub-type classification. Ni and Co contents of kamacite from several of the Type IIIs studied fall outside of the range for these elements in bulk meteoritic metal and are relevant to the assignment of a meteoritic vs a non-meteoritic origin for lunar metal particles in the fines and breccias.

Chromium and phosphorus enrichment in the metal of type II (C2) carbonaceous chondrites

Abstract Electron microprobe analyses of metal grains in nine C2 meteorites show consistently high Cr and P contents, with large grain to grain variations within individual meteorites. Cr ranges from 0.16 to 1.0 wt.% (average 0.6 per cent for 43 analyses). P ranges from 0.00 to 3.2 wt.% (average 0.42 per cent). In addition, metal grains in seven C3 meteorites show a lesser enrichment of Cr, 0.00 to 0.7 per cent (average 0.13 per cent for 59 analyses), with no P present. Both of these elements, Cr and P, are generally below detection in the metal of other chondrite groups, equilibrated and unequilibrated. C2 metal grains occur typically as spherical to ovate blebs contained within single, euhedral forsterite crystals or crystal fragments that are either isolated in the black C2 matrix or are in clusters making up white inclusions. Metal is rare within true chondrules. Calculations of the expected Cr contents in metal condensing directly from a solar nebular gas agree remarkably well with the observed values. Unfortunately, no calculation is possible for P because of insufficient data at the present time. The composition and the textural relationships indicate this Cr, P rich metal, and the enclosing forsterite are direct condensates from a cooling solar nebula. Cr and P, in the quantities reported here, characterize C2 metal.