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NASA NTRS1985

Concentrations and behavior of oxygen and oxide ion in melts of composition CaO.MgO.xSiO2

The behavior of oxygen and oxide ion in silicate melts was investigated through their electrochemical reactions at a platinum electrode. Values are given for the diffusion coefficient for molecular oxygen in diopside melt and the activation energy of diffusion. It is shown that molecular oxygen dissociates prior to undergoing reduction and that oxide ion reacts quickly with silicate polymers when it is produced. The concentration of oxide ion is kept low by a buffering effect of the silicate, the exact level being dependent on the silicate composition. Data on the kinetics of reaction of the dissociation of molecular oxygen and on the buffering reactions are provided. It is demonstrated that the data on oxygen in these silicate melts are consistent with those for solid buffers.

Semkow, K. W.↗

NASA NTRS1985

A refractory inclusion in the Kaba CV3 chondrite - Some implications for the origin of spinel-rich objects in chondrites

The first detailed petrographic and mineralogical study of a Ca, Al-rich inclusion (CAI) from the Kaba CV3 chondrite is reported. This 'fine-grained' CAI contains abundant small, rounded, rimmed, spinel-rich objects which have important features in common with the spinel-rich objects in other carbonaceous and ordinary chondrites. These nodules are interpreted as fractionated distillation residues of primitive dust. However, the available data do not unambiguously rule out a condensation origin for at least some of these objects. Finally, the preservation of distinct diopside-hedenbergite rims on the spinel-rich bodies and the small grain size of many minerals in the CAI matrix material both suggest that the CAI accreted cool and had a relatively cool thermal history in the Kaba parent body.

Fegley, B., Jr.↗

NASA NTRS1987

Experimental geochemistry of Pu and Sm and the thermodynamics of trace element partitioning

An experimental study of the partitioning of Pu and Sm between diopside/liquid and whitlockite/liquid supports the hypothesis that Pu behaves as a light rare earth element during igneous processes in reducing environments. D-Pu/D-Sm is found to be about 2 for both diopsidic pyroxene and whitlockite, and the amount of fractionation would be decreased further if Pu were compared to Ce or Nd. Data indicate that temperature, rather than melt composition, is the most important control on elemental partitioning, and that P2O5 in aluminosilicate melts serves as a complexing agent for the actinides and lanthanides.

Jones, John H.↗

NASA NTRS1988

Igneous history of the aubrite parent asteroid - Evidence from the Norton County enstatite achondrite

Numerous specimens of the Norton County enstatite achondrite (aubrite) were studied by optical microscopy, electron microprobe, and neutron-activation analysis. Norton County is found to be a fragmental impact breccia, consisting of a clastic matrix made mostly of crushed enstatite, into which are embedded a variety of mineral and lithic clasts of both igneous and impact melt origin. The Norton County precursor materials were igneous rocks, mostly plutonic orthopyroxenites, not grains formed by condensation from the solar nebula. The Mg-silicate-rich aubrite parent body experienced extensive melting and igneous differentiation, causing formation of diverse lithologies including dunites, plutonic orthopyroxenites, plutonic pyroxenites, and plagioclase-silica rocks. The presence of impact melt breccias (the microporphyritic clasts and the diopside-plagioclase-silica clast) of still different compositions further attests to the lithologic diversity of the aubrite parent body.

Okada, Akihiko↗

NASA NTRS1988

The origin of type C inclusions from carbonaceous chondrites

The origin of type C inclusions found in carbonaceous chondrites and the relationship of the type C inclusions to other Ca- and Al-rich chondrules are discussed on the basis of major-element composition of these objects. The results on bulk composition analysis of primary phase assemblages in eight Allende-type inclusions and an Allende glass-spinel inclusion were found to be consistent with the following scenario: (1) the condensation of melilite + spinel + perovskite +/- hibonite +/- CaAl4O7; (2) the reaction of melilite + spinel with SiO2(g); (3) the removal of inclusions from further interaction with the reacting gas; (4) melting with little or no volatilization; (5) crystallization; (6) alteration; and (7) incorporation of inclusions into host meteorite. Type C inclusions are considered to be precursors to Al-rich chondrules in ordinary and enstatite chondrites, i.e., they are considered to be a spinel-rich class of type A that reacted with silica from a coexisting gas to produce anorthite plus diopside.

Beckett, John R.↗

NASA NTRS1988

Petrology and physical conditions of metamorphism of calcsilicate rocks from low- to high-grade transition area, Dharmapuri District, Tamil Nadu

Calc-silicate rocks comprising quartz, plagioclase, diopside, sphene, scapolite, grossularite-andradite and wollastonite occur as lensoid enclaves within the greasy migmatitic and charnockitic gneisses of the Archaean amphibolite- to granulite-facies transition zone in Dharmapuri district, Tamil Nadu. The calc-silicate rocks are characterized by the absence of K-feldspar and primary calcite, presence of large modal quartz and plagioclase and formation of secondary garnet and zoisite rims around scapolite and wollastonite. The mineral distributions suggest compositional layering. The chemical composition and mineralogy of the calc-silicate rocks indicate that they were derived from impure silica-rich calcareous sediments whose composition is similar to that of pelite-limestone mixtures. From the mineral assemblages the temperature, pressure and fluid composition during metamorphism were estimated. The observed mineral reaction sequences require a range of X sub CO2 values demonstrating that an initially CO2-rich metamorphic fluid evolved with time towards considerably more H2O-rich compositions. These variations in fluid composition suggest that there were sources of water-rich fluids external to the calc-silicate rocks and that mixing of these fluids with those of calc-silicate rocks was important in controlling fluid composition in calc-silicate rocks and some adjacent rock types as well.

Narayana, B. L.↗

NASA NTRS1989

Steps toward interstellar silicate dust mineralogy

One of the most certain facts on interstellar dust is that it contains grains with silicon oxygen tetrahedra (SOT), the internal vibrations of which cause the well known silicate bands at 10 and 18 microns. The broad and almost structureless appearance of them demonstrates lack of translation symmetry in these solids that must be considered amorphous or glassy silicates. There is no direct information on the cations in these interstellar silicates and on the number of bridging oxygens per tetrahedron (NBO). Comparing experimental results gained on amorphous silicates, e.g., silicate glasses, of cosmically most abundant metals (Mg, Fe, Ca, Al) with the observations is the only way to investigate interstellar silicate dust mineralogy (cf, Dorschner and Henning, 1986). At Jena University Observatory IR spectra of submicrometer-sized grains of pyroxene glasses (SSG) were studied. Pyroxenes are common minerals in asteroids, meteorites, interplanetary, and supposedly also cometary dust particles. Pyroxenes consist of linearly connected SOT (NBO=2). In the vitreous state reached by quenching melted minerals, the SOT remain nearly undistorted (Si-O bond length unchanged); the Si-O-Si angles at the bridging oxygens of pyroxenes, however, scatter statistically. Therefore, the original cation oxygen symmetry of the crystal (octahedral and hexahedral coordination by O) is completely lost. The blended bands at 10 and 18 microns lose their diagnostic differences and become broad and structureless. This illustrates best the basic problem of interstellar silicate mineral diagnostics. Optical data of glasses of enstatite, bronzite, hypersthene, diopside, salite, and hedenbergite have been derived. Results of enstatite (E), bronzite (B), and hypersthene (H) show very good agreement with the observed silicate features in the IR spectra of evolutionarily young objects that show P-type silicate signature according to the classification by Gurtler and Henning (1986). Compositional parameters and main characteristics of experimental SSG spectra in IR for the glasses E, B, and H are shown in tabular form. Results fit excellently the relations derived by Koike and Hasegawa (1987) and suggest that the band ratio of the astronomical silicate by Draine and Lee (1984) is too low.

Dorschner, J.↗

NASA NTRS1991

Enstatite chondrites and achondrites as asteroidal resources

The highly reduced nature of the enstatite meteorites (chondrites and achondrites) differs from that of all other types of stony meteorites. The silicates in the enstatite meteorites contain almost no FeO. In addition, many normally lithophile elements such as Na, Ca, Mg, Cr, and Ti display chalcophilic behavior. A study of the chemistry and mineralogy of the enstatite meteorites was undertaken to determine their resource potential. On average, about 99 percent of the volume of an enstatite achondrite, or aubrite, consists of only four silicate minerals: enstatite, Na-rich plagioclase, diopside, and forsterite, with enstatite being by far the most abundant mineral. The remaining one percent of the volume consists of troilite, kamacite, and trace amounts of oldhamite, daubreelite, ferromagnesian albandite, and schreibersite. Thus, the aubrites can be considered as a possible source for large quantities of Mg, Si, and O, but are of little interest as a source of anything else. The enstatite chondrites appear to be more promising candidates for resource utilization. The chondrites are generally divided into two groups: EH (high iron, fine-grained, with abundant chondrules); and EL (low iron, coarse-grained, with little or no evidence of chondrules). Metallic Ni-Fe makes up roughly 20-25 weight percent of each type of enstatite chondrite. These meteorites are also a good source of nitrogen. This is due in part to the presence of osbornite and sinoite. The latter mineral is restricted to EL chondrites, which typically have a higher bulk nitrogen content than the EH chondrites. Three valuable metals, Cr, Mn, and Ti, are concentrated in a few distinct sulfide phases in the enstatite chondrites. These sulfide phases are troilite and niningerite in EH chondrites and troilite, daubreelite, and ferroan alabandite in EL chondrites.

Hutson, M. L.↗

NASA NTRS1991

Near-Earth and near-Mars asteroids: Prognosis of pyroxene types

The diagnostic signs of ferrous absorption band at 505nm and color index (u-x) found at main-belt asteroids and 6-parametric classification of light stone meteorites have been the basis of the work. The colorimetric data of light near-Earth and near-Mars asteroids from TRIAD and ECAS were analyzed. Composition fields of pyroxenes were obtained for these asteroids by the value of (u-x) and 505-nm ferrous absorption band position within the pyroxenes quadrilateral. Pyroxenes of the S-asteroids from Apollo-Amor which have spectral parameters similar to achondrites may be presented by the diopside series.

Shestopalov, D. I.↗

NASA NTRS1991

Numerical modeling of solidification and convection in a viscous pure binary eutectic system

The solidification and convection of the pure binary eutectic silicate system diopside-anorthite (Di-An) is numerically modeled. A mass-weighted enthalpy of fusion is used to account for the second solid phase (An) which crystallizes at the solidus temperature. Variable under-relaxation is used to aid convergence of the momentum equations in the implementation of the SIMPLER algorithm used to solve the two-dimensional continuum conservation equations. Numerical experiments of the solidification of Di80 melt show that a large temperature drop occurs across the solid and mush regions which decreases convective vigor in the liquid. Interesting compositional segregation patterns are produced during the solidification of Di80.

Oldenburg, Curtis M.↗

NASA NTRS1992

Solubility and partitioning of Ne, Ar, Kr, and Xe in minerals and synthetic basaltic melts

The solubilities of Ne, Ar, Kr, and Xe gases were measured in natural samples of anorthite, diopside, forsterite, spinel, and synthetic basaltic melts, the samples which represent equilibrium pairs in the Fo-An-Di-SiO2 system. Results show that, in natural minerals, the solubilities of these gases increase with increasing atomic number. In contrast, the solubilities of noble gases in the synthetic basaltic melts decreased with increasing atomic number. The partition coefficients increased with increasing atomic number for all mineral/melt pairs.

Broadhurst, C. L.↗

NASA NTRS1992

A unique, (almost) unaltered spinel-rich fine-grained inclusion in Kainsaz

A unique, spinel-rich, extremely porous fine-grained inclusion in the Kainsaz (CO3) meteorite is reported. This inclusion is the least altered fine-grained inclusion yet discovered, having escaped almost entirely the secondary alterations experienced by Allende fine-grained inclusions. The inclusion is comprised of loosely packed 5-30 microns spinel grains mantled by thin layers of melilite, anorthite, and diopsidic pyroxene. The inclusion, which has over 30 vol pct void space, is one of the most spinel-rich, most porous fine-grained inclusions seen to date. The mineralogy of the inclusion matches that which has been predicted for a precursor of the altered mineral assemblages of Allende fine-grained inclusions, though a lack of interstitial material in the Kainsaz inclusion reduces the likelihood of a direct genetic relationship between the two (Allende fine-grained inclusions contain abundant interstitial material). Its mineralogical composition confirms that the precursors of other, more altered, fine-grained inclusions were assemblages of refractory minerals exclusively.

Holmberg, B. B.↗

NASA NTRS1992

Mineralogy, petrology and geochemistry of carbonaceous chondritic clasts in the LEW 85300 polymict eucrite

We have performed a detailed petrologic and mineralogic study of two chondritic clasts from the polymict eucrite Lewis Cliff (LEW) 85300, and performed chemical analyses by INAA and RNAA on one of these. Petrologically, the clasts are identified and are composed of dispersed aggregates, chondrules, and chondrule fragments supported by matrix. The aggregates and chondrules are composed of olivine, orthopyroxene, plus some diopside. The matrix consists of fine-grained olivine, and lesser orthopyroxene and augite. Fine-grained saponite is common in the matrix. The bulk major composition of the clast studied by INAA and RNAA shows unusual abundance patterns for lithophile, siderophile and chalcophile elements but is basically chondritic. The INAA/RNAA data preclude assignment of the LEW 85300,15 clast to any commonly accepted group of carbonaceous chondrite.

Zolensky, M. E.↗

NASA NTRS1993

The solubility of gold in silicate melts: First results

The effects of oxygen fugacity and temperature on the solubility of Au in silicate melts were determined. Pd-Au alloys were equilibrated with silicate of anorthite-diopside eutectic composition at different T-fO2 conditions. The behavior of Au was found to be similar to that of Pd reported recently. Au solubilities for alloys with 30 to 40 at. percent Au decrease at 1400 C from 12 ppm in air to 160 ppb at a log fO2 = -8.7. The slope of the log(Me-solubility) vs. log(fO2) curve is close to 1/4 for Au and the simultaneously determined Pd suggesting a formal valence of Au and Pd of 1+. Near the IW buffer Pd and Au solubilities become even less dependent on fO2 perhaps reflecting the presence of some metallic Au and Pd.

Borisov, A.↗

NASA NTRS1993

Igneous fractionation and subsolidus equilibration of diogenite meteorites

Diogenites are coarse-grained orthopyroxenite breccias of remarkably uniform major element composition. Most diogenites contain homogeneous pyroxene fragments up to 5 cm across of Wo2En74Fs24 composition. Common minor constituents are chromite, olivine, trolite and metal, while silica, plagioclase, merrillite and diopside are trace phases. Diogenites are generally believed to be cumulates from the eucrite parent body, although their relationship with eucrites remains obscure. It has been suggested that some diogenites are residues after partial melting. I have performed EMPA and INAA for major, minor and trace elements on most diogenites, concentrating on coarse-grained mineral and lithic clasts in order to elucidate their igneous formation and subsequent metamorphic history. Major element compositions of diogenites are decoupled from minor and trace element compositions; the latter record an igneous fractionation sequence that is not preserved in the former. Low equilibration temperatures indicate that major element diffusion continued long after crystallization. Diffusion coefficients for trivalent and tetravalent elements in pyroxene are lower than those of divalent elements. Therefore, major element compositions of diogenites may represent means of unknown portions of a cumulate homogenized by diffusion, while minor and trace elements still yield information on their igneous history. The scale of major element equilibration is unknown, but is likely to be on the order of a few cm. Therefore, the diogenite precursors may have consisted largely of cm-sized, igneously zoned orthopyroxene grains, which were subsequently annealed during slow cooling, obliterating major element zoning but preserving minor and trace incompatible element zoning.

Mittlefehldt, David W.↗

NASA NTRS1994

Compositional variations of olivines and pyroxenes in chondritic interplanetary dust particles

We report here analyses of olivines and pyroxenes, and petrofabrics of 27 chondritic interplanetary dust particles (IDPs), comparing those from anhydrous and hydrous types. Approximately 40% of the hydrous particles contain diopside, a probable indicator of parent body thermal metamorphism, while this mineral is rarely present in the anhydrous particles. Based on this evidence, we find that hydrous and anhydrous IDPs are, in general, not directly related, and we conclude that olivine and pyroxene major-element compositions can be used to help discriminate between IDPs that are (1) predominantly nebular condensates, and lately resided in anhydrous or icy (no liquids) primitive parent bodies, and (2) those originating from more geochemically active parent bodies (probably hydrous and anhydrous asteroids).

Zolensky, Michael E.↗

NASA NTRS1998

Osmium Solubility in Silicate Melts: New Efforts and New Results

In a recent paper, Borisov and Palme reported the first experimental results on the partitioning of Os between metal (Ni-rich OsNi alloys) and silicate melt of anorthite-diopside eutectic composition at 1400 C and 1 atm total pressure and and at function of O2 from 10(exp -8) to 10(exp -12) atm. Experiments were done by equilibrating OsNi metal loops with silicate melt. Metal and glass were analyzed separately by INAA. D(sup 0s) ranged from 10(exp 6) to 10(exp 7), which is inconsistent with core/ mantle equilibrium for HSEs and favors the late veneer hypothesis. Unfortunately, there was practically no function of O2 dependence of Os partitioning, and the scatter of experimental results was quite serious, so the formation of Os nuggets was suspected. This new set of experiments was specifically designed to avoid of at least minimize the nugget problem

Borisov, A.↗

NASA NTRS2002

Bilanga: A Unique Diogenite

The Bilanga diogenite is petrographically examined and found to contain diopside and plagioclase aggregates up to several 100 microns in size. Small scale, original igneous contacts between these phase are often preserved despite brecciation. Additional information is contained in the original extended abstract.

Kolar, S. E.↗