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C. L. Christ

Publications and source records attributed to C. L. Christ.

18 recordsLinked to original sources
USGS1977

A crystal-chemical classification of borate structures with emphasis on hydrated borates

The rules governing formation of hydrated borate polyanions that were proposed by C.L. Christ in 1960 are critically reviewed and new rules added on the basis of recent crystal structure determinations. Principles and classifications previously published by others are also critically reviewed briefly. The fundamental building blocks from which borate polyanions can be constructed are defined on the basis of the number n of boron atoms, and the fully hydrated polyanions are illustrated. Known structures are grouped accordingly, and a shorthand notation using n and symbols ?? = triangle, T = tetrahedron is introduced so that the polyanions can be easily characterized. For example, 3:??+2T describes [B3O3(OH)5]2-. Correct structural formulas are assigned borates with known structures whereas borates of unknown structure are grouped separately. ?? 1977 Springer-Verlag.

Physics and Chemistry of Minerals↗
USGS1974

Stabilities of calcite and aragonite

A revaluation of the 25° C activity-product constants of calcite ( K C ) and aragonite ( K A ) was made on the basis of the known solubilities of these phases for which the activity of total dissolved calcium was corrected for the presence of the ion pair CaHCO 3 + in the aqueous phase. The value of the dissociation constant of CaHCO 3 + was taken to be 10 -1.225±0.02 . This value, combined with values of the analytical concentrations in solutions with partial pressure P CO2 =0.97 atmosphere, leads to K C =l0 -8.52±0.04 and K A = 10 -8.36±0.04 . Based on these K values, standard free energies of formation of calcite and aragonite were calculated to be -270,144±375 and -269,926±375 calories mole -1 , (-1,130,282±1,569 and -1,129,370±1,569 joules mole -1 ), respectively. From the 25°C K values, using appropriate entropy and heat capacity data, values of K C and K A were calculated over the temperature range 0° to 200°C. Possible errors in interpretation of measured pH values and inferred P CO2 values and the bearing of these errors on calculations of K values are discussed.

Journal of Research of the U.S. Geological Survey↗
USGS1974

Activity-product constants of aragonite at 90° and 51°C

The activity-product constants of aragonite, K A =[Ca 2+ ][CO 3 2- ] (where the brackets denote activities), were determined experimentally at 90°C and at 51°C. Results at 90°C were obtained from four separate dolomite dissolution runs, in which aragonite precipitated and came to equilibrium with the aqueous phase (from the direction of. supersaturation), and from two runs starting with aragonite suspended in dilute MgCl 2 solutions (from the direction of undersaturation). The average values of K A from the six runs were in excellent agreement; for the negative logarithm of K A , P K A , they yield a value of 8.95±0.05. One run was made at 51° C starting with aragonite suspended in dilute MgCl 2 solution; the value of p K A at 51°C is 8.61±0.05. No X-ray detectable calcite was found at the conclusion of any of the runs, including a dolomite dissolution run at 90°C (D-10) that was sampled over a period of 10,268 h and toward the end had a concentration of approximately 0.002 molal total dissolved magnesium.

Journal of Research of the U.S. Geological Survey↗
USGS1973

New data on cuprobismutite

Cuprobismutite from Tunnel Extension Number Two mine, Ohio mining district, Utah, was chemically analyzed using the electron microprobe. Its empirical formula was determined to be Cu 20.8 Ag 0.97 Pb 0.35 Mn 0.22 Bi 26.7 Sb 0.06 Te 0.05 Se 0.55 S 50.4. The tentative conclusion is that unsubstituted cuprobismutite has the chemical formula 6Cu 2 S*6Bi 2 S 3 rather than the previously ascribed formula 6Cu 2 S*6Bi 2 S 3 and that cuprobismutite is therefore not dimorphous with emplectite.

Utah↗
USGS1968

Studies in the system MgO-SiO2-CO2-H2O(I): The activity-product constant of chrysotile

Chrysotile dissolves congruently in water according to the reaction: Mg 3 Si 2 O 6 ( OH ) 4 c + 5 H 2 O l = 3 Mg aq 2+ + 6 OH aq − + 2 H 4 SiO 4 aq . Experimental determination of the activity-product constant of chrysotile, K chr = [ Mg 2+ ] 3 [ OH − ] 6 [ H 4 SiO 4 aq ] 2 , at 90°C, yields the value of K chr = 10 −49.2 ± 10 0.5 . A synthetic sample and a natural sample from New Idria, California, were used in the determination. Values of K chr were calculated for temperatures ranging from 0°C to 200°C, using the thermochemical data of King et al . (1967) for chrysotile and antigorite, various solubility data for silica, and ionic partial molal heat capacities estimated by the method of criss and Cobble (1964a). K chr is 10 −54.1 at 0°C, rises to a maximum value of 10 −48.5 at approximately 135°C, and is 10 −49.1 at 200°C (all values for the three-phase system, chrysotile plus solution plus vapor). The calculated 90°C value is 10 −49.1 , in excellent agreement with the experimental value; for 25°C, the calculated value is 10 −50.8 .

Geochimica et Cosmochimica Acta↗
USGS1968

Chemical potential of water from measurements of optic axial angle of zeolites

Values of the uncorrected optic axial angle (2H α ) of a crystal of the calcium zeolite stellerite (CaAl 2 Si 7 O l8 · 7H 2 0) immersed in calcium chloride solutions of known activity of water (a w ) are directly proportional to log a w . A general relationship between the chemical potential of water in the crystal and the optic axial angle is obeyed.

Science↗
USGS1964

Crystal chemistry and structure refinement of five hydrated calcium borates

The crystal structures of the five known members of the series Ca 2 B 6 O 11 ·xH 2 O (x = 1, 5, 5, 7, 9, and 13) have been refined by full-matrix least-squares techniques, yielding bond distances and angles with standard errors of less than 0·01 Å and 0·5°, respectively. The results illustrate the crystal chemical principles that govern the structures of hydrated borate compounds. The importance of hydrogen bonding in the ferroelectric transition of colemanite is confirmed by more accurate proton assignments.

Journal of Inorganic and Nuclear Chemistry↗
USGS1958

Mineralogical applications of electron diffraction. 1. Theory and techniques

The small wavelengths used in electron-diffraction experiments and the thinness of the crystals necessary for the transmission of the electron beam combine to require a somewhat different diffraction geometry for the interpretation of electron-diffraction patterns than is used in the interpretation of X-ray diffraction patterns. This geometry, based on the reciprocal lattice concept and geometrical construction of Ewald, needed for the interpretation. of transmission electron-diffraction single-crystal patterns is here reviewed. Transmission electron-diffraction single-crystal patterns of two monoclinic substances, colemanite [CaB 3 O 3 (OH) 3 •H 2 O] and potassium chlorate (KC10 3 ), are examined and the .theory necessary for their interpretation is given in detail. The study of these patterns furnishes a basis for the interpretation of single-crystal patterns of materials belonging to any crystal system. It is shown that useful unit-cell data, accurate to a few tenths of a percent, can be obtained from the patterns of colemanite and KClO 3 . A method of evaluating unit-cell data from measurements of such single-crystal patterns is given. The transmission electron-diffraction powder pattern obtained from an oriented aggregate of thin crystals gives the same unit-cell data as are given by the electron-diffraction single-crystal pattern obtained from one crystal of the aggregate., A graphical method is given for precisely evaluating unit-cell constants from measurements of such a powder pattern.

Trace Elements Investigations↗
USGS1956

Some observations on rutherfordine

The optical properties of rutherfordine, UO 2 CO 3 , previously determined on microscopic crystals, have been redetermined on considerably larger crystals; and the relations among the indices of refraction, the morphology, and the crystal structure have been examined. Rutherfordine is orthorhombic, biaxial positive, with α = 1.715, β = 1.730, γ = 1.795, 2V = 53° (calc.); X = b, Y = c (elongation, Z = a. The crystal structure of UO 2 CO 3 consists of layers of carbonate groups parallel to (010) with linear (O-U-O) ions normal to the layers. The indices β and γ correspond to vibration directions parallel to layers; the unexpectedly large difference in value between β and γ is ascribed to the optical anisotropy of the uranium-oxygen bonding in the layer. Indexed X-ray powder data are given.

Trace Elements Investigations↗
USGS1956

Behavior of Colorado Plateau uranium minerals during oxidation

Uranium occurs as U(VI) and U(IV) in minerals of the Colorado Plateau ores. The number of species containing U(VI) is large, but only two U(IV) minerals are known from the Plateau: uraninite, and oxide, and coffinite, a hydroxy-silicate. These oxidize to yield U(VI) before reacting significantly with other mineral constituents. Crystal-structure analysis has shown that U(VI) invariable occurs as uranyl ion, UO 2 +2 . Uranyl ion may form complex carbonate or sulfate ions with resulting soluble compounds, but only in the absence of quinquevalent vanadium, arsenic, or phosphorous. In the presence of these elements in the +5 valence state, the uranyl ion is fixed in insoluble layer compounds formed by union of uranyl ion with orthovanadate, orthophosphate, or orthoarsenate. Under favorable conditions UO 2 +2 may react to form the relatively insoluble rutherfordine, UO 2 CO 3 , or hydrated uranyl hydroxides. These are rarely found on the Colorado Plateau as opposed to their excellent development in other uraniferous areas, a condition which is apparently related to the semiarid climate and low water table of the Plateau. Uranium may also be fixed as uranyl silicate, but little is known about minerals of this kind. In the present study emphasis has been placed on a detailing of the chemical and crystal structural changes which occur in the oxidation paragenetic sequence.

Utah↗