Richard S. Mitchell

Mineralogy of ash of some American coals: variations with temperature and source

Abstract Ten samples of mineral-matter residue were obtained by the radio-frequency low-temperature ashing of subbituminous and bituminous coals. The low-temperature ash samples were then heated progressively from 400 °C to 1400 °C at 100 °C intervals. Mineral phases present at each temperature interval were determined by X-ray diffraction analyses. The minerals originally present in the coals (quartz, kaolinite, illite, pyrite, calcite, gypsum, dolomite, and sphalerite) were all altered to higher temperature phases. Several of these phases, including kaolinite, metakaolinite, mullite, anhydrite, and anorthite, were found only in limited temperature ranges. Therefore the temperature of formation of the ashes in which they occur may be determined. Mineralogical differences were observed between coal samples from the Rocky Mountain Province, the Illinois Basin, and the Appalachians; and as a result of these mineralogical differences, different high-temperature phases resulted as the samples were heated. However, regional generalizations cannot be made until a greater number of samples have been studied.

Structural polytypism of tin disulfide: Its relationship to environments of formation

Abstract Conditions during growth have a strong influence upon the formation of different polytypic structures of SnS2. Weissenberg X-ray diffraction photographs were made of 250 crystals, 25 from each of ten different growth environments. The greatest differences are observed between crystals grown by chemical transport reactions, without halogen, or with iodine or bromine. Environments without halogen favored 2H at lower temperatures (ca. 600°C), 18R at intermediate temperatures, and 4H at higher temperatures (ca. 800°C). In other experiments, the presence of iodine seems to contribute to the formation of the 18R type as well as rare complex polytypes and disordered structures. Those grown with bromine as a carrier only had the 2H structure. Crystals grown from an As2S3 flux were mainly 2H while those formed from the cooling of a stoichiometric melt were primarily 18R. The temperature of final crystallization seems to be a major factor in these last two cases. Representative crystals from all environments showed growth spirals. It is concluded that polytypism in SnS2 is influenced by the following factors: temperature of formation, presence of impurities (iodine), and very likely spiral growth from screw dislocations (especially in the rare complex polytypes).

Order hardening in equiatomic CuPt

Samples of equiatomic CuPt were quenched from above the ordering temperature into icy brine, annealed at 300°, 500°, and 700°C, and examined by microhardness, optical microscope, electron microscope, and X-ray diffraction techniques. In samples annealed for short times at 300° and 500°C a fine-domained mottled structure consisting of all four orientation variants of the ordered cell is seen. Continued annealing produces a coarsedomained grain boundary component which X-ray diffraction shows to have a higher degree of order than the mottled structure. At lower temperatures the grain boundary component grows and replaces the mottled structure to complete the ordering transition. At high temperatures the mottled structures coarsen into order twins lying on (110) and (100) type planes. The transformation to order and the resulting hardness changes are seen to depend largely on the internal strains resulting from the cubic to rhombohedral distortion.

Tridymite Pseudomorphs after Wood in Virginian Lower Cretaceous Sediments

Fossil wood composed of tridymite is abundant in Patuxent (Lower Cretaceous) arkose on Hazel Run, Fredericksburg, Virginia. X-ray diffraction studies of the tridymite indicate that it has a disordered structure in which hexagonal close packing predominates. The specimens, which contain trace amounts of aluminum, iron, and other elements, are soft and fibrous, varying from white to shades of brown.

Who's Who in Mineral Names: Sidney Arthur Williams (1933–), James Dwight Dana (1813–1895)

(1988). Whos Who in Mineral Names: Sidney Arthur Williams (1933–), James Dwight Dana (1813–1895) Rocks & Minerals: Vol. 63, No. 1, pp. 36-39.

Who's Who in Mineral Names

In addition to being an executive editor for Rocks and Minerals, Richard S. Mitchell is the author of the books Dictionary of Rocks and Mineral Names: What Do They Mean?, both published by Van Nostrand Reinhold.

Who's Who in Mineral Names: Henry Samuel Delinde (b. 1923), Orlando J. Benston (1901–1966), Joseph Wood Kimzey (1888–1975) and Members of the Kimzey Family, the Honorable Elias William Rector (1849–1917), Hugh Dinsmore Miser (1884–1969)

Delindeite, (Na,K)2.7(Ba,Ca)4(Ti,Fe,AI)6Si8O26(OH)14, was found in the Diamond Jo quarry, Hot Spring County, Arkansas, as aggregates of flakelike crystallites in compact spherules, light pinkish gray in color with a resinous, pearly luster. The mineral forms under oxidizing weather conditions.