Milton Blander

The origin of meteorites and the constrained equilibrium condensation theory

Abstract Microscopic examination and microprobe analyses were made in individual chondrules in unequilibrated meteorites. Our observations as well as published data are compared with the predictions and consequences of the “constrained equilibrium” theory of Blander and Katz. The large variety of textures of chondrules is shown to be consistent with the postulate that chondrules were formed as subcooled liquid drops. The distribution and concentrations of oxidized and metallic iron in equilibrated and unequilibrated chondrites are consistent with constraints imposed by nucleation kinetics and the consequent supersaturation of iron vapor during the condensation process. The different contents of volatile elements of different chondrites fits the theory in a simple manner consistent with the calculations of Larimer and Anders by taking into account the relative rates of accretion and rates of cooling of the gas which governed the condensation and incorporation of elements of different volatility. Most of the compositional and textural features in chondrites thus could have been formed during the condensation and accretion processes in a cooling nebula.

The thermodynamics of cluster formation in nucleation theory

We have derived a precise thermodynamic definition of the standard free energy to form a cluster which is used in nucleation theory. The results [Eq. (9)] have a form differing slightly from the form usually used in nucleation theory and show that the Lothe-Pound correction factor is based on a misconception concerning the standard states involved.

The constrained equilibrium theory: Sulphide phases in meteorites

Abstract The constraints imposed by nucleation kinetics are taken into account in calculations of the condensation of sulfide phases from a gas of solar composition. Troilite will condense from a gas supersaturated with respect to metallic iron at temperatures which are much higher than from a gas at equilibrium with iron. In a solar gas at relatively high pressures, where we postulate that the precursors of the enstatite chondrites form, liquid troilite is condensed. At lower pressures of a solar gas, where we postulate that the precursors of the ordinary chondrites form, solid troilite is condensed. The solid does nob accommodate significant amounts of some sulfides in solid solution at activities less than unity and some chalcophilic elements will not tend to co-condense. On the other hand, liquid troilite can accommodate significant concentrations of sulfides in solution at activities less than unity and other chalcophile elements will co-condense. The apparently anomalous differences in the content of some chalcophile elements which have been observed between the enstatite and ordinary chondrites and the occurrence of oldhamite and niningerite are consistent with our calculations. Some implications and predictions concerning the genesis of sulfide and metal phases which result from our calculations will be discussed.

Use of a CO2 laser to prepare chondrule-like spherules from supercooled molten oxide and silicate droplets.

Abstract Chondrule-like spherules were formed from individual freely falling subcooled droplets of alumina, enstatite, forsterite, enstatite-albite and forsterite-albite mixtures that had been melted with a focused continuous CO2 laser beam. Their textures (rimmed, excentro-radial, barred, glassy) are strikingly similar to those of many meteoritic chondrules. It is suggested that the phenomena associated with rapid crystallization from the supercooled melt are responsible for the various textures observed in the artificial spherules as well as in similar meteoritic chondrules. Although our experiments involve fast crystallization of rapidly cooling molten droplets in an ambient medium of low temperature and, hence, resemble the conditions that might apply to chondrule formation by small-scale thermal events produced by, for example, volcanism, impact splattering or electrical discharge processes, it is suggested that the textures observed would also result from rapid crystallization of relatively slowly cooling molten droplets that may have been produced in larger scale events, including condensation from a nebula of solar composition and solidification in an ambient medium of high temperature.

Mössbauer Spectroscopy of Moon Samples

Lunar bulk sample 10084,85 (< 1 mm size dust), and samples from rocks 10017,17 (fine grained, vesicular), 10046,17 (breccia), 10057,59 (fine grained, vesicular, top surface), 10057,60 (fine grained, vesicular, interior), and 10058,24 (medium grained, not vesicular) have been investigated by 57Fe M�ssbauer spectroscopy. Iron metal and the Fe2+ minerals ilmenite, pyroxene, troilite, and iron containing glass have been identified. An iron line of sample 10084,85 (originally sealed in nitrogen) showed no significant intensity change when the sample was exposed to air. The antiferromagnetic transition in several lunar ilmenites at 570 � 2�K corresponds to stoichiometric FeTiO,. Magneticallv separated 10057 showed troilite and somne metallic iron.

Heating of basalts with a carbon dioxide laser

Basalts heated strongly with focused infrared laser radiation vaporized and splattered. Electron microprobe analyses of condensate, ejecta, and residue show strong vapor fractionation trends which, for some elements, are different from what would be expected theoretically and from previously reported data on more siliceous materials. It appears that solution effects can account for these differences. Heating of materials by a powerful focused laser beam for the purpose of study of vapor fractionation is a convenient technique that is more versatile than previous methods such as heating in solar or arc image furnaces.

The partitioning of cations between coexisting one site-two site phases

Abstract Simplified equations are derived for the description of the partitioning of cations between coexisting one-site and two-site phases. The equations can be utilized for the analysis of data on the distribution of cations between olivine and pyroxene.

Mössbauer Investigation of Apollo 11 Lunar Samples

Mossbauer spectroscopy has been used to study samples of lunar dust and rocks returned on the Apollo 11 mission. In addition to iron metal, the Fe2+ minerals ilmenite, pyroxene, troilite, and iron-containing glass were identified. There was no evidence for Fe3+ or for unusual iron charge-state ions. Heavy liquids were used to separate the dust into fractions of differing specific-gravity ranges. The light part, which contained most of the glass, also contained most of the iron metal. The antiferromagnetic transition in the ilmenite of the dust and rocks was investigated by the constant-velocity counting rate method. All samples studied had transition temperatures of 57° ± 2°K, corresponding to stoichiometric FeTiO3. A magnetically separated sample of rock 10057 was used to clarify the nature of the magnetically ordered phases in the rocks, principally troilite with minor amounts of iron metal. As illustrated by the ilmenite iron to silicate iron ratio, the compositions of the dust and breccia were similar, but differed significantly from the typical rock compositions.