The Journal of Geology

doi: 10.1086/627122pmid: N/A

Subsolidus phase relations in the ternary systems $$CaCO_{3}-MgCO_{3}-CoCO_{3} and CaCO_{3}-MgCO_{3}-NiCO_{3}$$ have been investigated at 600°, 650°, 700°, and 750° C. in the system containing cobalt and at 600°, 700°, and 750° C. in the system with nickel. All the runs were made in squeezer-type equipment, for the most part at 15 kb. applied pressure. Equilibrium could not readily be attained at temperatures below 600° C. Decomposition was a constant source of difficulty, particularly in runs rich in $$NlCO_{3}$$, and higher pressures were required in some cases. The configuration of the system with $$CaCO_{3}$$ is similar to the system $$CaCO_{3}-MgCO_{3}-FeCO_{3}$$, although solid solubility of $$CoCO_{3}$$ in calcite and dolomite is somewhat less than FeCOe at equivalent temperatures. A three-phase area (cobaltoan-magnesian calcite, calcian-magnesian cobaltocalcite, and cobaltoan dolomite) is still present at 750° C, and at all temperatures there are also three two-phase areas and three single-phase areas (Co, Mg-calcites, complete $$MgCO_{3}-CoCO_{3}$$ solid solutions, and a thin field of cobaltoan dolomites). The system containing $$NiCO_{3}$$ is more complex; solid solubility is quite limited, and a solubility gap interrupts the $$MgCO_{3}-NiCO_{3}$$ binary system, producing two three-phase areas (both containing nickeloan dolomite, differing slightly in composition). In addition there are four small single-phase fields and five two-phase fields. It has been shown that the dolomite-type compound $$CaFe(CO_{3})_{2}$$ is not stable. Similarly the compounds $$CaCo(CO_{3})_{2} and CaNi(CO_{3})_{2}$$ do not exist. The solubility of $$CoCO_{3}$$ in dolomite at 750° C. is slightly more than 25 mole per cent and of $$NiCO_{3}$$ approximately 15 per cent.

doi: 10.1086/627123pmid: N/A

In order to provide a basis for calibration of X-ray-emission analyses, existing theories and experimental measurements on the generation, absorption, and fluorescence of X-rays produced by electron bombardment of mixed targets are reviewed and compared with new measurements for a variety of targets, principally common silicates. Theoretically, the efficiency of X-ray generation should depend strongly on the mean atomic number of a mixed target, and its variation is commonly described by a so-called atomic-number factor. Using hard radiation for which the absorption is trivial, measurements have shown that the Philibert factor (1 + h) varies too little with mean atomic number. A new empirical factor, $$[4.7 + 0.9 In (V_{0} - V_{k}) - In {\langle}Z{\rangle}] {\langle}Z/A {\rangle} R^{-1}$$ fits the data to within 2 per cent, except for $$V_{0}$$ close to $$V_{k}$$ ($$V_{0}$$is incident electron accelerating voltage in kilovolts, $$V_{k}$$ is ionization voltage for K-electrons, {\langle}Z{\rangle} is mean atomic number of target weighted according to mass concentration, {\langle}Z/A{\rangle} is a similar average for ratio of atomic number to atomic weight, R is Green's backscatter coefficient to express proportion of potential ionization energy retained in target). For soft radiation, empirical absorption curves have been derived for simple and complex oxides on the assumption that the above efficiency-of-generation factor is valid. These curves differ markedly from those suggested by measurements on single-element targets, and it is recommended that the new curves be used for analyses in which the same experimental conditions are used. It is concluded that analyses of major elements in common minerals can be carried out to a relative accuracy of 1-5 per cent by suitable choice of standards and experimental conditions; such conditions are described.

doi: 10.1086/627126pmid: N/A

The Littlewood Nunataks located in Coats Land near Duke Ernst Bay on the eastern edge of the Filchner Ice Shelf were visited in January, 1959, and rock samples were collected. Petrographic and chemical analyses show the rock to be a rhyolite porphyry with a minimum K-Ar age of $$840 \pm 30$$ m.y. Rock samples from nearby nunataks collected and examined by two Argentine parties are similar except for a limestone specimen. If the limestone is associated with the rhyolite as some data indicate, then these rocks may represent an interbedded sequence of Precambrain subaqueous lavas and marine sediments. The rhyolite porphyry and associated rocks have been designated the Littlewood Volcanics. The relationship of the Littlewood Volcanics to rock units of the nearby Transantarctic Mountains is obscure, but the Littlewood Volcanics are tentatively placed among the older of two pre-Beacon rock groups because of age, geographic location, and degree of metamorphism.