Geology topics

James J. McGee

Publications and source records attributed to James J. McGee.

3 recordsLinked to original sources

USGS1990

The thermodynamic properties of dumortierite Si 3 B[Al 6.75 [] 0.25 O 17.25 (OH) 0.75 ]

The heat capacities of dumortierite have been measured from 7 to 1000 K by quasiadiabatic low-temperature and differential scanning calorimetry. The corrected calorimetric entropy at 298.15 K calculated from the experimental data is 330.2 + 5.0 J/(mol.K) based upon the chemistry of the sample, average compositions proposed by Alexander et al. (1986), and correction to the structural formula given by Moore and Araki (1978). Moore and Araki (1978) have shown the Al(l) site to be disordered, and chemical analyses suggest that there is some Al substitution for Si. A minimum configurational entropy of 4.74 J/(mol'K) should be added to the corrected calorimetric entropy for third law calculations. The enthalpy and Gibbs free energy of formation of dumortierite from the elements have been estimated from synthesis and decomposition data and are -9109 + 20 and -8568 + 20 kJ/mol, respectively, at 298.15 K and I bar

American Mineralogist↗

USGS1987

Inter-laboratory comparison of X-ray fluorescence analyses of eruptive products of El Chichón Volcano, Chiapas, Mexico

An inter-laboratory comparison has been made of X-ray fluorescence analyses of 10 samples of lava and pumices from El Chichón Volcano, Chiapas, Mexico. Some determinations of major-element constituents agree within analytical uncertainty, whereas others exchibit significant bias. Analyses carried out at the Michigan Technological University (MTU) laboratory are systematically lower in MgO (26–48%), Fe total (5–18%), CaO (4–15%) and higher in K 2 O (0–15%) than analyses made at the U.S. Geological Survey (USGS) Denver laboratory. These differences are ascribed in part to a complex combination of calibration assumptionsand mineralogical and particle-size effects inherent in the use of pressed rock-powder pellets in the analytical procedure of the MTU laboratory. Other, but as yet unknown, differences in sample preparation and/or analytical technique may also be important; effects related to natural sample inhomogeneityare believed to be insignificant. The inter-laboratory differences in the analytical data complicated accurate assessment of whether El Chichón magmas have changed composition during the past 300 000 a. Knowledge of such change is needed for understanding petrogenetic history and for such related studies as evaluation of volcanic hazards.

Applied Geochemistry↗

USGS1983

$ANBA; a rapid, combined data acquisition and correction program for the SEMQ electron microprobe

$ANBA is a program developed for rapid data acquisition and correction on an automated SEMQ electron microprobe. The program provides increased analytical speed and reduced disk read/write operations compared with the manufacturer's software, resulting in a doubling of analytical throughput. In addition, the program provides enhanced analytical features such as averaging, rapid and compact data storage, and on-line plotting. The program is described with design philosophy, flow charts, variable names, a complete program listing, and system requirements. A complete operating example and notes to assist in running the program are included.

Open-File Report↗