High-pressure reactions and shear strength of serpentinized dunite.

The recently reported Pronounced decrease in shear strength of serpentine-bearing rocks at 30 to 40 kilobars in the temperature range 300 degrees to 520 degrees C may be attributed to the transformation of serpentine to a Pressure-dependent, 10-angstrom,2: 1 layer silicate plus brucite and periclase. This reaction increases density by about 8.5 percent.

Indium Telluride (II'): Transitory Intermediate Phase in the Transformation InTe(II) to InTe(I).

The high-pressure cubic metallic form of indium telluride, InTe(II), transforms at 1 atmosphere to a new transitory polymorph, designated InTe(II'), which, in turn, transforms to the stable tetragonal polymorph InTe(I). The new polymorph is apparently tetragonal with unit-cell dimensions a(0) = 6.06 A, c(0) = 6.

Stishovite: Thermal Dependence of the Crystal Habit.

The crystal habit of stishovite changes with the temperature of crystallization at a pressure of about 120 kb. Below 600 degrees C it is bipyramidal; between 600 degrees and 900 degrees C it is granular; and above 900 degrees C it is acicular. This temperature dependence of the crystal habit of stishovite may constitute a highpressure geological thermometer which could indicate limiting values for the peak temperatures that prevailed at craters of meteoritic origin in highly siliceous rocks.

High-Pressure Metallic Indium Telluride: Preparation and Crystal Structure.

The metallic high-pressure form of indium telluride may be prepared under high pressure at 150 degrees C and retained at ambient conditions without low-temperature quenching. It has the NaCl (type B1) structure with a cell edge of 6.160 +/- .

Phase Composition of Commercial "Ammonium Carbonate".

A unique crystalline phase was the sole constituent in newly opened containers of commercial reagent-grade "ammonium carbonate." The chemical composition, optical constants, x-ray powder diffraction pattern, infrared absorption spectrum, and density indicate a double salt, ammonium bicarbonate-carbamate (NH(4)HCO(3).NH(4) CO(2)NH(2)), which is unstable in air at ambient temperature and decomposes rapidly to ammonium bicarbonate.

Relation of Infrared Spectra to Coordination in Quartz and Two High-Pressure Polymorphs of SiO2.

Infrared spectra of the four-coordinated quartz and coesite polymorphs of SiO(2), the rutile six-coordinated (stishovite) polymorph of SiO(2), and the quartz and rutile polymorphs of GeO(2) show that a change from tetrahedral to octahedral cation coordination results in (i) a 23-per-cent increase in the wavelength of the main absorption band for both the SiO(2) and GeO(2) polymorphs and (ii) a significant increase in the force constant of the same magnitude for the SiO(2) and GeO(2) polymorphs. The quartz and the rutile isostructural pairs for SiO(2) and GeO(2) show that the effect of increasing mass is to increase proportionally the wavelength of the respective main absorption bands. The infrared data for the rutile form of SiO(2) fit the empirical equation of Dachille and Roy relating cation coordination, mass, atomic number, valence, and main absorption wavelength.