Search Results - (Author, Cooperation:N. Z. Boctor)

2012-05-26

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Carbon/*analysis ; Crystallization ; Extraterrestrial Environment ; *Mars ; *Meteoroids ; Organic Chemicals/*analysis ; Oxidation-Reduction ; Oxides/analysis ; Polycyclic Hydrocarbons, Aromatic/*analysis/chemistry ; Silicates/*chemistry ; Spectrum Analysis, Raman

1432-0967

Springer Online Journal Archives 1860-2000

Geosciences

Abstract Abundant small xenoliths in the Mzongwana kimberlite dike, Transkei, southern Africa, are predominantly pyroxenites composed of ilmenite, pyrope, orthopyroxene, clinopyroxene, rutile, and phlogopite; two of the xenoliths contain small amounts of Ti-rich amphibole near kaersutite in composition. A majority of the pyroxenites have polygonal granoblastic textures, but many have fasciculate, acicular and skeletal growths. The latter are believed to be the product of rapid crystallization because of similarities to textures of lunar and terrestrial volcanic rocks and quenched experimental charges. Segregations of garnet or ilmenite and pyroxene are common, and these are believed to have originated by crystallization from supersaturated magma. Pyroxenes in the rocks that appear to have crystallized most rapidly are richer in Al and Ti and the garnets are richer in Ti than comparable phases in the granoblastic rocks. The Mzongwana kimberlite is estimated to have a minimum depth of origin of 150 km by application of pyroxene thermobarometry to bronzite discrete nodules. The depth of crystallization of the pyroxenite xenoliths is believed to be near 100 km on the basis of comparison with phase relations determined by experiment. The pyroxenites appear to have crystallized from Ti-rich, olivine-free magma that was probably derived from a kimberlitic parent. A basaltic source (Karoo?), however, is not ruled out. Rapid crystallization of the pyroxenites at depth in the mantle may have occurred by intrusion in thin dikes some days prior to inclusion in erupting kimberlite. Alternatively, the kimberlite may have incorporated a pyroxenitic liquid, either derivative or unrelated, that crystallized through loss of volatiles and heat in contact with the expanding kimberlite vapor phase. The compositions of the minerals in the Mzongwana pyroxenites are similar to those of Fe-rich discrete nodules that occur in many other kimberlites. Perhaps the minerals in the pyroxenites and the discrete nodules have similar origins except that the Mzongwana pyroxenites crystallized more rapidly at shallower depths in the mantle.

Electronic Resource

1432-1866

Springer Online Journal Archives 1860-2000

Geosciences

Abstract Sulfide minerals in coal bed III at the Chinook Mine, Indiana, are pyrite, marcasite, and rarely sphalerite. Pyrite occurs as framboids concentrated mainly in exinite, as bands or lenses in vitrinite and clay partings, as cell fillings in fusinite, and in cleats. Marcasite normally occurs in association with clusters of pyrite framboids within micro-organic remains. Sphalerite occurs exclusively in fusinite associated with cleat pyrite. The iron sulfides, which are of authigenic origin, were formed during the biochemical stage of coalification during the accumulation and compaction of peat. The factor that limited their formation in such an environment was the availability and reactivity of iron. Chemical heterogeneity in the peat swamps where the sulfides formed existed even on a microscopic scale. The iron sulfides were commonly precipitated in localized micro-environments that were favorable for their formation. The metamorphic stage of coalification did not affect the iron sulfides significantly, although it may have been responsible for the recrystallization of pyrite framboids and minor deformation of pyrite in fusinite and its local mobilisation.

Electronic Resource