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NASA NTRS1973

Armalcolite and genetically associated opaque minerals in the lunar samples

A comprehensive electron microprobe study of armalcolite in samples from five Apollo sites (11-16), together with analytical data previously reported from Apollo 17 and Luna 20 show that three distinct compositional types of armacolite are present in the lunar samples. These types are classified as armalcolite, Cr-Zr-Ca-armalcolite and Zr-armalcolite. The Zr-free armalcolites are typical of high-Ti mare basalts whereas the Zr-rich armalcolites are typical of non-mare high alumina basalts. The latter armalcolites are in complete oxide intergrowths (baddeleyite, zirconolite, rutile, ilmenite, and chromite) and are in contrast to the Zr-free armalcolites which are commonly only associated with ilmenite. Subsolidus decomposition of armalcolite to an iron and Mg-rich rutile + ilmenite-geikielite, and the solid state formation of armalcolite from magnesium-ilmenite + niobian-rutile are described for the first time in the lunar samples.

Haggerty, S. E.↗

NASA NTRS1973

Rust in the Apollo 16 rocks

Apollo 16 samples of all four rock types and from all stations contain evidence for hydration and oxidation - i.e., the presence of hydrated iron oxide, probably goethite. Rock 66095 contains native FeNi grains with a characteristic intergrowth of schreibersite and, to lesser extents, of cohenite. Troilite also contains sphalerite. The goethite contains 1.5-4.6 wt.% chlorine and occurs mainly on the edges of FeNi metal, causing a rust color in the cracks and space around the native metal grains, which also contain abundant chlorine. This observation suggests the presence of lawrencite (FeCl2), a phase that deliquesces and oxidizes very rapidly upon exposure to water or to a moist atmosphere.

Taylor, L. A.↗

NASA NTRS1976

Lodestone: Nature's own permanent magnet

Magnetic hysteresis and microstructural details are presented which explain why the class of magnetic iron ores defined as proto-lodestones, can behave as permanent magnets, i.e. lodestones. Certain of these proto-lodestones which are not permanent magnets can be made into permanent magnets by charging in a field greater than 1000 oersted. This fact, other experimental observations, and field evidence from antiquity and the middle ages, which seems to indicate that lodestones are found as localized patches within massive ore bodies, suggests that lightning might be responsible for the charging of lodestones. The large remanent magnetization, high values of coercive force, and good time stability for the remanent magnetization are all characteristics of proto-lodestone iron ores which behave magnetically as fine scale ( 10 micrometer) intergrowths when subjected to magnetic hysteresis analysis. The magnetic results are easily understood by analysis of the complex proto lodestone microstructural patterns observable at the micrometer scale and less.

Wasilewski, P.↗

NASA NTRS1976

Microcracks, micropores, and their petrologic interpretation for 72415 and 15418

Lunar samples 72415 and 15418 have complex microstructures that indicate a series of fracturing and healing events. Both samples contain relatively few open microcracks but many sealed and healed microcracks. Dunite 72415 contains abundant healed cracks that formed tectonically, symplectic intergrowths spatially and probably genetically related to microcracks, and a cataclastic matrix that has been extensively sintered. Metamorphosed breccia 15418 contains many post-metamorphic healed cracks, large shock induced cracks that have been sealed with glass, and a few younger, thin, open shock induced cracks.

Richter, D.↗

NASA NTRS1977

Magnetic and microstructural properties of some lodestones

A lodestone is an iron ore that behaves as a permanent magnet. A protolodestone is an iron ore capable of being charged sufficiently strongly to behave as a permanent magnet. In the present paper, important criteria are established which distinguish lodestones from other iron ores. Magnetic hysteresis-loop data provide evidence that the massive pieces of lodestone behave magnetically as fine intergrowths rather than coarse multidomain material. This means that the iron ores have been magnetically hardened. The nature and scale of the hardening microstructure is illustrated by photo micrographs. The mechanism of charging the protolodestone appears to be either transient magnetic fields with lightning-discharge currents, or presently obscure aspects of magnetization intensity enhancement associated with maghemitization of massive iron ores.

Wasilewski, P. J.↗

NASA NTRS1978

Tysnes Island - An unusual clast composed of solidified, immiscible, Fe-FeS and silicate melts

An inclusion found in the Tysnes Island gas-rich H4 chondrite is described. The clast consists of two distinct portions, separated by a smooth boundary; the portions are a tear-drop shaped Fe-FeS eutecticlike intergrowth (0.5 cm greatest dimension) and a silicate consisting primarily of olivine in glass. Nickel enrichment is found in the metal at the metal-sulfide boundaries and in nodules within the metal. It is thought that the portions separated from one another as immiscible liquids and that the modal composition of each portion agrees with the compositions predicted for a total melt of an H-group chondrite. The inclusion is discussed in terms of the process of metal-silicate fractionation suggested by Fodor and Keil (1976).

Wilkening, L. L.↗

NASA NTRS1977

Petrology of four clasts from consortium breccia 73215

One felsite ('granite') and three ANT-suite anorthositic gabbro clasts extracted from breccia 73215 are described. The felsite clast has two components - fragments of crystalline felsite and veins and patches of felsic glass. The crystalline felsite, which consists largely of a vermicular intergrowth of quartz and Ba-K-feldspar, crystallized from a highly differentiated melt between 3.90 and 4.05 b.y. The felsic glass component consists of crystallized brown and colorless glasses and uncrystallized colorless glass which are all K and Si rich. The relation of glass features to past heating and the breccia-forming event is considered. In the three anorthositic gabbros, which have similar mineralogies and gradational textures, plagioclase is dominant, and olivine and orthopyroxene are the major mafic minerals. The petrologic data suggest that the gabbros formed as heated, partly melted, and/or recrystallized polymict breccias. It is possible that the approximately 4.25 b.y. age obtained for the three rocks is the date of the melting/recrystallization event.

James, O. B.↗

NASA NTRS1979

Lodestone-explanation for magnetic properties and characterization of the source of magnetic hardening

The microstructure of Class I lodestones was investigated by X-ray diffraction and by optical and transmission electron microscopy, and the behavior of lodestone magnetization was studied at temperatures of 4 to 825 K. It was found that intense magnetization is associated with the gamma Fe2O3-Fe3O4 intergrowth. Thermal demagnetization of the lodestone studied was nearly complete at 300 C. The loss of natural remanence was found to be associated with transformation of gamma Fe2O3 to alpha Fe2O3.

Wasilewski, P. J.↗

NASA NTRS1978

Metamorphic effects in experimentally heated Krymka /L3/ chondrite

Experimental charges of the Krymka unequilibrated ordinary chondrite heated from 500-1000 C have been examined petrographically for evidence of metamorphism. Of the petrologic criteria commonly used to distinguish types 4-6 chondrites, only changes in opaque mineral compositions are observed. Chemical and textural observations indicate development of a fine-grained intergrowth of taenite + troilite beginning at 700 C due to melting within the metal-rich portion of the Fe-Ni-S system, and minor reduction of troilite to metal, possibly through sulfur loss at higher temperatures. Overall textural integration, glass devitrification, and significant Fe-enrichment of ferromagnesian minerals are not observed because the short duration of these experiments was not sufficient for the development of other changes normally attributed to metamorphism in ordinary chondritic meteorites.

Mcsween, H. Y., Jr.↗

NASA NTRS1979

New phyllosilicate types in a carbonaceous chondrite matrix

Observations of new types of layer silicates in the crystalline regions of the matrix of a carbonaceous chondrite are reported. Ion-thinned sections of the Murchison meteorite were observed by high-resolution transmission electron microscopy. Images obtained of patterns of fringe spacings of 4.9 and 7.3 A are interpreted as resulting from ordered and disordered sequences of brucite-like and serpentine-like layers, respectively. The temperature and pressure conditions of phyllosilicate formation in the Murchison matrix are discussed in light of the suggested crysotile serpentine and brucite layers and evidence of Fe and Al in the layered intergrowths.

Mackinnon, I. D. R.↗

NASA NTRS1979

Apollo 12 feldspathic basalts 12031, 12038 and 12072 - Petrology, comparison and interpretations

The paper presents the petrology of Apollo 12 feldspathic basalts. Modal and chemical data indicate that basalts 12072, 12038, and 12031 cannot be related to the other Apollo rock types; 12072 contains phenocrysts of olivine and pigeonite, 12038 is a multiply saturated equigranular basalt, and 12031 is a coarse-grained rock with granular to graphic intergrowths of pyroxene and plagioclase. The bulk compositions indicate that these basalts could not have been derived from the Apollo 12 olivine or ilmenite basalts by crystal-liquid fractionation, and their petrologic similarities suggest that they were produced in the same or similar source regions.

Beaty, D. W.↗

NASA NTRS1982

Origin of rapidly solidified metal-troilite grains in chondrites and iron meteorites

Quantitative evidence is adduced by cooling rate calculations for the impact melting, on the surface of a parent body, of troilite and metallic Fe, Ni inclusions found on 12 ordinary chondrites rather than their formation at depth from an internally derived melt. In the case of the Shaw and Rose City breccias of unmelted and melted material, their melted metal need not have cooled through 1000 C within a few meters of the surface. Shock-melted, fine-grained, irregular intergrowths of metal and troilite form in situ in many irons and some chondrites by rapid solidification at cooling rates greater than 100,000 C/sec, so that their kamacite and taenite compositions may result from annealing of metallic glass or very fine quench products at about 250 C.

Scott, E. R. D.↗

NASA NTRS1982

A new LL3 chondrite, Allan Hills A79003, and observations on matrices in ordinary chondrites

Allan Hills A79003 is an LL3 chondrite with a petrologic subtype of 3.4 + or - 0.2. Contrary to previous suggestions, it is not paired with other Allan Hills specimens. It contains haxonite, (Fe,Ni)23C6; shock-melted, 'fizzed' metal-troilite intergrowths; and translucent, glassy-looking Huss matrix (fine-grained, Fe-rich silicate matrix), in addition to the normal opaque and recrystallized varieties of Huss matrix. Some chondrules are partly coated with opaque matrix, others with translucent matrix. Translucent matrix is more uniform in composition and contains less S, CaO and FeO and more MgO than the opaque variety. Both kinds of matrix rimmed chondrules before consolidation of the meteorite.

Scott, E. R. D.↗

NASA NTRS1983

A new layered mineral from the Mighei carbonaceous chondrite

The poorly characterized phase (PCP) of the Mighei CM2 carbonaceous chondrite is investigated using high-resolution TEM. Electron-microprobe analyses of samples from both olivine chondrules and the matrix are included in a table. Chondrule PCP is found to have higher concentrations of S and Ni and lower concentrations of Si, Mg, and Al than matrix PCP. TEM shows that PCP in this chondrite is an intergrowth of three phases (in various proportions): a major component containing Fe, S, Ni, and O in wavy rolled layers spaced about 5.4 A apart, an Fe-rich serpentinelike phyllosilicate with 7-A layer spacing, and submicron grains of magnetite, chromite, and phosphate. It is proposed that chondrule PCP contains mainly the 5-A phase with some grains, while matrix PCP consists mostly of the 5-A and 7-A phases.

Tomeoka, K.↗

NASA NTRS1983

On the alteration of Allende chondrules and the formation of matrix

Recent SEM observations of the Allende chondrules and matrix are reported. Intergrowths of both Fe-rich olivine (with a composition near Fa50), and clinoenstatite (with a composition of about Fs2). All of the clinoenstatite was involved in associations along the outer margins, grain boundaries, and internal crack surfaces of the chondrule. Most of the chondrules also contain abundant opaque inclusions which must have been strongly altered and partially replaced before chondrule formation. It is suggested that the Fe-rich olivine formed from the clinoenstatite by a reaction of the type Fe + 1/202 + MgSiO3 to (Fe,Mg)2SiO4. It is argued that a variation of the small, internally-heated planetesimal provides the most plausible environment for the chemical reaction.

Housley, R. M.↗

NASA NTRS1985

Accretionary rims on inclusions in the Allende meteorite

The origin and composition of the rim sequence on the refractory inclusion in the Allende meteorite are studied. The different textures, mineralogy, and mineral-chemistry of the four layers of the rim are described. The layers are composed of: pyroxene, needles, olivine, hedenbergite, and andradite. Tables of the element and chemical compositions of the layers are presented. The data reveals that: (1) the layers are highly porous masses of euhedral crystals with no intergrowth; (2) layers contain highly disequilibrium mineral assemblages; and (3) the thickness of the layers varies with the underlying topography. These results support the theory that rim structures are accretionary aggregates formed from accretion of independently grown particles onto the surface of inclusions. The formation of the grains in the layers and matrix from nebular condensates is studied.

Macpherson, G. J.↗

NASA NTRS1986

Refractory minerals in interplanetary dust

A newly studied interplanetary dust particle contains a unique set of minerals that closely resembles assemblages in the refractory, calcium- and aluminum-rich inclusions in carbonaceous chondrite meteorites. The set of minerals includes diopside, magnesium-aluminum spinel, anorthite, perovskite, and fassaite. Only fassaite has previously been identified in interplanetary dust particles. Diopside and spinel occur in complex symplectic intergrowths that may have formed by a reaction between condensed melilite and the solar nebula gas. The particle represents a new link between interplanetary dust particles and carbonaceous chondrites; however, the compositions of its two most abundant refractory phases, diopside and spinel, differ in detail from corresponding minerals in calcium- and aluminum-rich inclusions.

Christoffersen, Roy↗

NASA NTRS1987

Pristine moon rocks - A 'large' felsite and a metal-rich ferroan anorthosite

Results of elemental analyses, performed either by instrumental neutron activation analysis (NAA) or radiochemical NAA, of 19 lunar rock samples obtained by the Apollo 15, 17, and 12 missions are presented. Two of the samples are most extraordinary: 'large' (1 g) felsite from Apollo 12 and a pristine ferroan anorthosite from Apollo 15. The felsite is mainly a graphic intergrowth of K-feldspar and a silica phase, with about 6 pct plagioclase and 1 pct each of ferroaugite, ilmenite, and fayalitic olivine. The Fe-metal content of ferroan anorthosite is 1.2 wt pct in the thin section studied (but, based on mass balance for Co and Ni, must have been lower in the chip used for bulk-rock analysis); the measured bulk-rock concentrations of siderophile elements Re, Os, and Ir are far higher than previously observed among pristine lunar anorthosites. These results underscore the uncertainty associated with any attempt to estimate the overall siderophile element contents of the moon's crust.

Warren, Paul H.↗