Edward J. Dwornik

Transformation of montmorillonite to kaolinite during weathering

Extensive deposits of kaolinite in Florida are formed by transformation of montmorillonite during low-temperature supergene weathering. The transformation occurs by intracrystalline leaching of interlayer cations and tetrahedral silica layers. Interposition of stripped layers within montmorillonite creates a regular 1:1 mixedlayered montmorillonite-kaolinite, a new clay structure. Kaolin-like layers are nourished by lateral epitaxy, as the iron-rich montmorillonite decomposes. Hexagonal outgrowths of new kaolinite develop at the edges of montmorillonite flakes and nucleate new vertical growth. Kaolinitic sands impregnated with goethite are ultimately formed, and the released silica enriches groundwater and forms secondary chert.

Primary Protodolomite in Echinoid Skeletons

Protodolomite has been identified in the teeth of Recent echinoids by means of electron microprobe and X-ray diffraction analyses. The analyses demonstrate a high degree of heterogeneity with respect to magnesium carbonate content in these skeletal parts; the entire spectrum of compositions between magnesium calcite and protodolomite was encountered.

Metallic Spherules in Tektites from Isabela, Philippine Islands

Iron-nickel spherules, as much as 0.5 mm in diameter, have been found completely embedded in some philippinites. The spherules consist mainly of kamacite with unidentified pink inclusions. The meteoritic origin of these spherules seems reasonable, suggesting that the tektites containing them were formed by asteroidal or meteoritic impact.

New data on the nickel-iron spherules from Southeast Asian tektites and their implications

Abstract This paper presents new occurrences and mineralogic, petrographic, and chemical data on metallic spherules found in Philippine tektites from the Ortigas site of Mandaluyong near Manila and in indochinites from Dalat, South Viet Nam. Most of the metallic spherules contain kamacite, schreibersite and troilite. Schreibersite and troilite occur interstitially or in blebs among round or elongate fine-grained matrix kamacite. Where abundant, schreibersite coalesces and forms a network throughout the entire spherule. Troilite generally occurs in small round droplets within the schreibersite. The amount of schreibersite varies from less than 5 to about 35 per cent by volume and the troilite may constitute as much as 5 per cent of the spherules. The composition of the phases present in the spherules was determined by the electron probe. In 9 analysed spherules from philippinites of the Ortigas site, the kamacite ranges from 1.6 to 4.5 per cent nickel. The average nickel content of kamacite in 3 analysed spherules from indochinites ranges from 4.7 to 12.9 per cent. The average nickel content in 4 schreibersite grains analysed from a single spherule ranges from 12.1 to 15.8 per cent. The spherules in the tektites are nearly identical with the meteoritic spheroids from Meteor Crater, Arizona, in texture, mineral assemblage and nickel content as shown by the new data. We conclude that these spherules were formed as molten droplets of an impacting meteoritic body which was instrumental in producing the tektite glass.

Pecoraite, Ni6Si4O10(OH)8, nickel analog of clinochrysotile, formed in the wolf creek meteorite

Pecoraite is a new phase in the natural system H2O-NiO-MgOSiO2, the nickel analog of clinochrysotile. It occurs in cracks in the Wolf Creek meteorite in Australia where it was formed under hydrothermal conditions. Particles of pecoraite are very small curved plates which have begun to coil; some have achieved spiral form.

Lunar clinopyroxenes: Chemical composition, structural state, and texture

Single-crystal x-ray diffraction, microprobe, optical and electron optical examinations of clinopyroxenes from Apollo 11 lunar samples 10003, 10047, 10050, and 10084 show that generally the crystals are composed of (001) augitepigeonite intergrowths in varying ratios. Transmission electron micrographs reveal abundant exsolution lamellae, many only 60 A thick. In addition to the phase inhomogeneities, primary chemical inhomogeneities are clearly demonstrated. There are reciprocal relationships between calcium and iron and between Ti4+ + 2Ai and 2Si. Our evidence suggests that a chemically inhomogeneous subcalcic C2/c augite was the only primary pyroxene from which pigeonite later exsolved.

Nickel-iron spherules from aouelioul glass.

Nickel-iron spherules, ranging from less than 0.2 to 50 microns in diameter and containing 1.7 to 9.0 percent Ni by weight, occur in glass associated with the Aouelloul crater. They occur in discrete bands of siliceous glass enriched in dissolved iron. Their discovery is significant tangible evidence that both crater and glass originated from terrestrial impact.

Naturally occurring vapor-liquid-solid (VLS) Whisker growth of germanium sulfide

Abstract The first naturally occurring terrestrial example of vapor-liquid-solid (VLS) growth has been observed in condensates from gases released by burning coal in culm banks. Scanning electron microscopy, X-ray diffraction, and energy dispersive analysis indicate that the crystals consist of elongated rods (≈ 100 μm) of germanium sulfide capped by bulbs depleted in germanium.

The detection of sulphur in contamination spots in electron probe X-ray microanalysis

Sulphur has been identified as one of the elements present in the contamination spot which forms under the electron beam in the microprobe. The presence of the sulphur results in a rapid change in intensity measurements causing a loss of observed intensity for elements other than sulphur. The source of sulphur has been traced at least in part to the Apiezon B diffusion pump oil. A comparative X-ray fluorescence study of the Apiezon B and Octoil diffusion pump oils showed substantial amounts of sulphur in the Apiezon B. The Octoil was relatively free of sulphur.