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All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

The effect of temperature and pressure on the distribution of iron group elements between metal and olivine phases in the process of differentiation of protoplanetary material

The distribution patterns of Ni, Co, Mn, and Cr were studied in olivines of various origins: from meteorites (chondrites, achondrites, pallasites), which are likely analogs of the protoplanetary material, to peridotite inclusions in kimberlite pipes, which are analogs of mantle material. According to X-ray microanalysis data, nickel is concentrated in peridotite olivines, while manganese is concentrated in meteoritic olivines. The maximum chromium content was found in ureilites, which were formed under reducing conditions. Experiments at pressures of 20 to 70 kbar and temperatures of 1100 to 2000 C have shown that in a mixture of olivine and Ni metal or NiO, nickel enters the silicate phase, displacing Fe into the metallic phase. Equilibrium temperatures were estimated from the Fe, Ni distribution coefficients between the metal and olivine: 1500 K for pallasites, 1600 K for olivine-bronzite H6 chondrites, 1200 K for olivine-hypersthene L6, 900 K for LL6, and 1900 K for ureilites (at P = 1 atm). The equilibrium conditions of peridotites are close to T = 1800 K and P over 100 kbar. It is concluded that there is a sharp difference between the conditions of differentiation of the protoplanetary material at the time meteorites were formed and the conditions of differentiation of the planets into concentric layers.

Vinogradov, A. P.↗
NASA NTRS1977

Olivine separates from Murchison and Cold Bokkeveld - Particle tracks and noble gases

Olivine separates from Murchison and Cold Bokkeveld were analyzed for particle tracks and noble gases. The matrix remaining after olivine separation was also analyzed for noble gases. The olivines from both meteorites have comparable fractions of solar-flare-irradiated grains, but the highest track densities in Murchison are an order of magnitude greater than those in Cold Bokkeveld. Solar Ne content in Murchison olivines follows this trend, being at least an order of magnitude higher than that in Cold Bokkeveld. Track gradients in Cold Bokkeveld olivines are flatter than those in Murchison or recently exposed lunar crystals. Relative to the matrix, olivine separates in both meteorites have small enrichments at the heavy and light Xe isotopes and smaller Ar-36/Ar-38 ratios. These noble-gas effects may be related to a chromite impurity in the olivine separates.

Macdougall, J. D.↗
NASA NTRS1980

The composition of mesosiderite olivine clasts and implications for the origin of pallasites

The composition of olivine clasts from the mesosiderites Emery, Mincy and Pinnaroo is investigated, and implications of the results for the origin of the pallasites, which, although chemically distinct, may be related to the diogenites, eucrites, howardites and mesosiderites, are discussed. Centimeter-sized olivines were analyzed by electron microprobe, and instrumental neutron activation analysis was performed on one olivine each from Emery and Pinnaroo and an olivine separate from the Brenham pallasite. The olivine compositions are found to range from Fa8 to Fa28, with Emery samples having values from Fa18 to Fa28, and to require essentially total melting of a source composition rich enough in FeO to produce basaltic clasts. It is argued that the mesosiderite olivines were formed in the outer few kilometers of their parent body, as were those of the pallasites, which have the same compositions as the mesosiderite olivines. A model is then developed for the origin of the pallasites as a by-product of igneous differentiation in the external heating of a chondritic parent body.

Mittlefehldt, D. W.↗
NASA NTRS1986

Mineralogy of interplanetary dust particles from the 'olivine' infrared class

Analytical electron microscopy observations establish that olivine is abundant and the predominant silicate phase in three interplanetary dust particles (IDPs) from the 'olivine' infrared spectra category. Two of the particles have microstructures resembling those of most nonhydrous chondritic IDPs, consisting of micron to submicron grains together with a matrix composed of amorphous carbonaceous material and sub-500 A grains. In addition to olivine these particles respectively contain enstatite and magnetite, and pentlandite plus Ca-rich clinopyroxene. The third IDP consists mostly of olivine and pyrrhotite with little or no matrix material. Olivine grains in this particle contain prominent solar-flare ion tracks with densities corresponding to a space-exposure age between 1000 to 100,000 years. Although the three particles have olivine-rich mineralogies in common, other aspects of their mineralogies and microstructures suggest that they experienced different formation histories. The differences between the particles indicate that the olivine infrared spectral category is a diverse collection of IDPs that probably incorporates several genetic groups.

Christoffersen, R.↗
NASA NTRS1993

Oxygen isotopic composition of individual olivine grains from the Allende meteorite

The oxygen isotopic composition of a variety of individual olivine grains (including refractory forsterite grains, cores of isolated olivine grains, FeO-rich rims, and individual matrix olivine grains) from the Allende CV3 meteorite was investigated by ion microprobe mass spectrometry, in order to obtain information on the formation mechanism of these samples. It was found that the most primitive (i.e., refractory) olivine in Allende is far less enriched in O-16 than are spinel and pyroxene in Ca,Al-rich inclusions, suggesting that Allende olivine must have formed in an environment that is less enriched in O-16 compared to the gas from which Ca,Al-inclusions are formed. FeO-rich (26-30 wt pct) rims of isolated olivine grains are significantly higher in delta-O-17 and delta-O-18 than forsteritic cores, suggesting that these rims formed by condensation from an oxidized gas with higher delta-O-17 than delta-O-18. Matrix olivine was found to be highest in FeO and to have the lowest enrichment in O-16.

Weinbruch, S.↗
NASA NTRS1993

Petrogenesis of Apollo 12 mare basalts. Part 1: Multiple melts and fractional crystallization to explain olivine and ilmenite basalt compositions

Mare basalts returned by the Apollo 12 mission have been divided into 4 groups on the basis of mineralogy and whole-rock chemistry: olivine basalts; pigeonite basalts; ilmenite basalts; and feldspathic basalts. James and Wright and Rhodes et al. concluded that the olivine and pigeonite groups were co-magmatic and that the within group variations are due to fractional crystallization of olivine and minor Cr-spinel, with pigeonite replacing olivine in the pigeonite basalts. Rhodes et al. concluded that the parental compositions for these suites were probably represented by the vitrophyres, and the olivine basalts are comprised essentially of cumulates and the pigeonites of evolved end-members. However, Neal et al. have demonstrated, using trace-element considerations, that the Apollo 12 olivine and pigeonite suites are not related. The ilmenite basalts were studied extensively by Dungan and Brown who noted that both cumulates and evolved fractionates were present within this group. In their modeling, Dungan and Brown used the vitrophyre compositions as parents. Neal et al. demonstrated that the feldspathic suite was probably comprised of only one member - 12038. Herein, the ilmenite and olivine basalts are demonstrated to be the products of several non-modal partial melting events of a single source followed by closed-system fractional crystallization.

Neal, Clive R.↗
NASA NTRS1993

Determining the composition of olivine on asteroidal surfaces

Olivine was remotely identified as a major component on many S- and A-type asteroids based on qualitative analyses of broad absorption features near 1.0 micron in their telescopic reflectance spectra. Laboratory studies showed that this diagnostic olivine absorption feature is composed of three individual absorption bands resulting from electronic transitions of Fe(+2) in distorted M1 and M2 sites. Both the overall absorption feature and each of the individual absorption bands are also known to vary systematically as a function of olivine composition. Thus, it should be possible to remotely determine the composition of olivine present on the surfaces of the various olivine-rich asteroids. However, extrapolation of laboratory studies to compositional interpretation of asteroid spectra is complicated by several factors: observational noise; lower spectral resolution; compositional heterogeneities (including the presence of other phases such as pyroxenes and/or metal); and the effects of alteration processes. In order to address such complex problems, a quantitative approach to spectral analysis, the modified Gaussian model (MGM) was developed by Sunshine et al., which deconvolves spectra into their constituent absorption bands. The MGM, a refinement of the Gaussian model, more accurately adheres to the physical processes involved in electronic transition absorptions. Under the MGM, each spectrum is modeled in log reflectance and energy as a sum of absorption bands superimposed onto a baseline or continuum. Each absorption band is described by three model parameters (center, width, and strength) which can be interpreted and used to infer composition. One of the strengths of the MGM is that it allows compositional information to be extracted directly from measured spectra and is therefore complementary to other approaches to modeling asteroid spectra which require the use of meteorites and/or terrestrial samples as spectral analogs. A quantitative understanding of the properties of olivine absorptions was established by using the MGM to analyze a laboratory suite of spectra spanning a full range of olivine compositions.

Sunshine, Jessica M.↗
NASA NTRS2017

Formation Mechanism of Iron-Rich Olivine: Experimental Constrains into Early Fluid-Assisted Hydration and Dehydration Processes on Asteroids

Iron-rich olivine is one of the major minerals in the matrices of unequilibrated ordinary (UOCs) and carbonaceous (CV, CK, CO) chondrites whose petrologic type is >3.1. There has been an extensive discussion in the literature as to the formation mechanism of these olivines; however, their origin is poorly understood. The formation of ferroan olivine during hydrothermal alteration has been demonstrated to be thermodynamically viable. The stability of ferroan olivine is highly dependent on several variables, including temperature, water/ rock (W/R) ratio, pressure, oxygen fugacity, and bulk rock composition. So far, hydrothermal alteration experiments have not been successful at forming FeO-rich olivines with the compositions and textures observed in the matrices of chondrites. Therefore, understanding the formation conditions of FeO-rich olivines remains a key problem to explain the effects of hydrothermal alteration on chondrite matrices.

Iron-rich olivine↗
NASA NTRS1976

An experimental investigation of olivine morphology

Results are reported for a morphological study of olivine and an experimental investigation performed to determine the degrees of supercooling and the cooling rates necessary to crystallize particular morphologies. Ten arbitrary categories of three-dimensional olivine crystal shape are identified: polyhedral, granular, hopper, chain, lattice, plate, branching, radiate, feather, and swallow-tail. The morphological study establishes that equant and tabular crystals are the common shapes of olivine, nonequant crystals are elongate parallel to the a or c axis, and skeletal crystals result when a particular form is missing or only partially developed. In the experiment, olivine crystals were grown by melting rock samples above their liquidus temperatures before initiating crystallization. The results show that olivine morphology changes systematically as a function of the degree of melt supercooling, the melt cooling rate, and the normative olivine and water contents of the melt. It is also found that each shape has a specific range of temperature stability which is essentially independent of melt composition.

Donaldson, C. H.↗
NASA NTRS1977

Coarse-grained basalt 71597 - A product of partial olivine accumulation

Rock 71597, a coarse-grained plagioclase-poikilitic basalt that contains 15.8% MgO and 19.3% modal olivine, is described. Olivine and ilmenite crystals occur in two size generations, and large subequant olivine crystals, small 'matrix' olivines, and large ilmenite crystals are characterized. Since large olivine and ilmenite crystals with skeletal habits suggestive of crystallization under relatively rapid cooling are found in a rock whose texture is consonant with slower cooling, it is suggested that the large skeletal crystals formed toward the more rapidly cooled margin of a flow and accumulated by gravitational crystal settling toward the flow's interior. In support of this hypothesis, calculations indicate that the observed olivine compositions are approximately 10 mol% too Fe-rich to have crystallized from a melt of composition corresponding to that of 71597.

Warner, R. D.↗
NASA NTRS1977

Examination of the liquid line of descent of mare basalts in light of data from melt inclusions in olivine

Data on 226 melt inclusions and their host olivines (173 new analyses) are presented and interpreted in terms of general liquid lines of descent and olivine fractionation. The melt inclusions in olivine along with those in ilmenite and late-stage mesostasis in mare basalts define a complex trend. The trend is complicated by the effects of ilmenite, plagioclase, and pyroxene fractionation within the melt inclusions in olivine, the fact that most of the basalts were multiply saturated during olivine fractionation, and the phenomenon of late-stage silicate immiscibility. It is suggested that the first two factors can account for the observed marked divergence of the melt inclusion data from simple early olivine fractionation trends. The elimination of the effects of daughter mineral fractionation by homogenization experiments is considered.

Weiblen, P. W.↗
NASA NTRS1980

Nepheline and sodalite in a barred olivine chondrule from the Allende meteorite

The discovery of nepheline and sodalite in association with glass in a barred olivine chondrule from the Allende C3V meteorite is reported, and the possible origin of the minerals is discussed. Scanning electron microscope/energy dispersive analysis indicates that the major minerals of the chondrule are olivine, bronzite and chromite, with olivine bars separated by glass of nearly pure plagioclase composition. The olivine is observed to have a composition richer in Fe than that predicted from olivine-liquid equilibria, indicating, along with the presence of plagioclase glass and small amounts of subcalcic diopside, the nonequilibrium crystallization of the barred olivine chondrule. The textural features of the chondrule are consistent with a liquid origin for nepheline and sodalite from the chondrule-forming liquid under nonequilibrium conditions.

Lumpkin, G. R.↗
NASA NTRS1992

On the relationship between isolated and chondrule olivine grains in the carbonaceous chondrite ALHA77307

The origin of the isolated olivine grains in carbonaceous chondrites was investigated by determining the zoning characteristics and the minor-element compositions of olivines from all the isolated and the chondrule occurrences in the ALHA77307 chondrite. The data obtained strongly suggest that, in ALHA77307, there is a genetic relationship between the isolated olivine grains and the chondrule population. Furthermore, the chondrule olivine compositions and zoning properties are consistent with the view that the isolated olivine grains were derived from chondrules and that most if not all isolated olivine grains formed due to crystallization from a liquid during chondrule formation.

Jones, Rhian H.↗
NASA NTRS1993

A comparison of FeO-rich, porphyritic olivine chondrules in unequilibrated chondrites and experimental analogues

Experimentally produced analogues of porphyritic olivine (PO) chondrules in ordinary chondrites provide an important insight into chondrule formation processes. We have studied experimental samples with PO textures grown at three different cooling rates (2, 5 and 100 C/h), and samples that have been annealed at high temperatures (1000-1200 C) subsequent to cooling. These are compared with natural chondrules of similar composition and texture from the ordinary chondrites Semarkona (LL3.0) and ALH 81251 (LL3.3). Zoning properties of olivine grains indicate that the Semarkona chondrules cooled at comparable rates to the experiments. Zoning in olivine from chondrules in ALH 81251 is not consistent with cooling alone but indicates that the chondrules underwent an annealing process. Chromium loss from olivine is very rapid during annealing and calculated diffusion coefficients for Cr in olivine are very similar to those of Fe-Mg interdiffusion coefficients under the same conditions. Annealed experimental samples contain an aluminous, low-Ca pyroxene which forms by reaction of olivine and liquid. No similar reaction texture is observed in ALH 81251 chondrules, and this may be evidence that annealing of the natural samples took place at considerably lower temperatures than the experimental analogues. The study supports the model of chondrule formation in a cool nebula and metamorphism of partly equilibrated chondrites during reheating episodes on the chondrite parent bodies.

Jones, Rhian H.↗
NASA NTRS1993

Angrite LEW87051: Are the olivines pheno's or xeno's? A continuing story

The achondrite LEW87051 is a porphyritic basalt consisting of large subhedral to euhedral zoned olivines in a finer-grained groundmass. The texture of this groundmass looks remarkably like a quenched melt. However, although the rock is clearly igneous, its exact origins and history are under dispute. From petrographic observations, Prinz felt that the large olivines were xenocrysts and that the zoning reflected interaction with an unrelated, CAI-enriched melt. McKay et al. was able to model the olivines as phenocrysts, whose zoning was the result of a parent melt that changed in composition as material crystallized, e.g., fractional crystallization in a closed system, and calculated a parent melt composition. Jurewicz and McKay compared the calculated parent melt composition with actual partial melts from CV and CM chondrites. They showed that the calculated melt was substantially different from equilibrium melts of these chondrites; however, the LEW87051 groundmass composition was similar to some of the low temperature partial melts, although slightly enriched in AN (or depleted in OL) components. This study presents the results of an independent petrologic look at other olivines in LEW87051 and the preliminary results of a quantitative model for the major zoning in these olivines as diffusive-exchange with an olivine-saturated, low temperature angritic melt.

Jurewicz, A. J. G.↗
NASA NTRS1993

A dynamic melting model for the origin of Apollo 15 olivine-normative and quartz-normative mare basalts

Early studies of mare basalts from the Apollo 15 site established that two distinct groups are represented: the olivine-normative basalts (ONB) and the quartz-normative basalts (QNB). The ONB and QNB suites are distinguished petrographically by their phenocryst assemblages (the ONB's are olivine-phyric, the QNB's are generally pyroxene-phyric) and chemically by their major element compositions: the QNB's are higher in SiO2 and MgO/FeO, and lower in FeO and TiO2 than ONB's with similar MgO contents. Experimental data show that the QNB suite is derived from a more magnesian, olivine-normative parent magma, a conclusion which is supported by the recent discovery of high-SiO2 olivine-normative basalt clasts in breccia 15498. The high-SiO2 ONB's fall on olivine control lines with primitive QNB's, and least-squares mixing calculations are consistent with the high-SiO2 ONB's being parental to the more evolved QNB suite. These high-SiO2 ONB's are included as part of the 'QNB suite'. Our major element modeling results also are consistent with the conclusions of earlier studies which showed that the ONB and QNB suites cannot be related to one another by low pressure crystal fractionation. The combination of high Mg#, high SiO2, and low TiO2 in the QNB suite precludes a relationship to the ONB suite by simple removal of liquidus minerals (olivine and pigeonite). Despite these significant differences in petrography and major element composition, both groups have nearly identical trace element concentrations and chondrite-normalized abundance patterns. The major question to be addressed by any petrogenetic model for Apollo 15 mare basalts is how to form mare basalt suites with distinctly different major element characteristics but nearly identical trace element compositions. The similarity in trace element concentrations imply compositionally similar source regions and similar percent melting, but these conclusions are not easily reconciled with the observed differences in major element compositions, which require sources with distinct mineralogies or large differences in percent melt.

Vetter, Scott K.↗
NASA NTRS1994

Diffusive modification of primary zoning in olivine cores in Angrite LEW 87051

Angrite LEW 87051 consists of large olivine crystals set in a fine-grained groundmass that clearly represents a crystallized melt. A few olivines contain Ca-poor, Cr-rich cores that crystallized from a very different melt than the outer part of the crystals constituting the majority of olivine in LEW 87051. We evaluate a model in which the cores formed through fractional crystallization of one melt, then were incorporated into a different melt as xenocrysts, whereupon the original zoning patterns were modified by diffusion. Using a similar approach, we calculate zoning patterns for the cores that would result from perfect fractional crystallization, compare them with the observed zoning, and determine whether the differences could result from diffusive modification consistent with known diffusion rates for Ca, Mn, and Cr. Using distribution coefficients from the 1400 C, IW + 1 experiments, we computed CaO, Cr2O3, and MnO abundances in the hypothetical parent melt by inverting the olivine at the centers of the cores. We further assumed that the primary zoning profile for CaO is essentially unmodified, because the diffusion rate of Ca in olivine is slow. We carried out the fractional crystallization calculation until the calculated Ca content was that observed at break in zoning profiles at the outer edge of the core. We then normalized the distance of this calculated profile to the length of the observed profile in the olivine core and calculated profiles for MnO and Cr2O3. The CaO zoning profile agrees well with the observed profile. The observed MnO profile is slightly higher than the calculated profile near the edge. Diffusion calculations indicate that reversal of the general trend of primary zoning through diffusion would require that diffusion of Cr is 5-10x faster than that of Mn.

Mikouchi, T.↗
NASA NTRS1999

Thermal Emission Spectroscopy of 1 Ceres: Evidence for Olivine

Thermal emission spectra of the largest asteroid 1 Ceres obtained from the Kuiper Airborne Observatory display features that may provide information on its surface mineralogy. A plot of the Ceres spectrum (calibrated using alpha Boo as a standard) divided by a standard thermal model (STM) is shown. Also shown is the emissivity spectrum deduced from reflectivity measurements for olivine grains <5 microns in diameter. The general shape of the Ceres and the olivine curves agree in essential details, such as the maxima from 8 to 12 microns, the minimum between 12 and 14 microns, the broad peak near 17.5 micron, and the slope beyond 22 micron. (Use of the 10 to 15-micron grain reflectivities provides a better match to the 12- to 14-micron dip. We used a value of unity for beta, the beaming factor associated with small-scale surface roughness in our STM. Adjustment of beta to a lower value raises the long-wavelength side of the Ceres spectrum, providing an even better match to the olivine curve.) The emissivity behavior roughly matches the emission coefficients which were calculated for olivine particles with a particle radius of 3 microns. Their calculations show not only the negative slope from 23 to 25 pm, but a continued decrease past 30 micron. The Ceres emissivity is thus similar to that of small olivine grains from 8 to 30 micron, but olivine's emissivity is lower from 5 to 8 pm.

Witteborn, F. C.↗