Tile crystal structures of sjogrenite and pyroaurite, two stacking modifications of approximate composition Mg.Fe.(OH),.(CO.).4H.O, have been determined by X-ray diffraction using three-dimensional methods. Sjogrenite is hexagonal, with a 3,13, C 15.66 A, space group P6.!mmc, Z = !; pyroaurite is rhombohedral, with aH 3,13, CH 23.49 A, space group R3m or R3m, Z = i. Both structures are based on...

This paper presents a mineralogical and chemical investigation of shale deposits from the U.S. Gulf coast in order to document the mechanisms and reactions involved in the diagenetic conversion of smectite into illite. Cuttings from the 1,250 to 5,500 m stratigraphic interval of a well were sorted by grain size and analzyed by x-ray diffraction to assess chemical and mineralogical trends with d...

of the International Mineralogical Association, 16th general meeting (1994), p. 40. 17. W. P. Grif® th, `̀ Raman Spectroscopy of Minerals’ ’ , in The Infrared Spectra of Minerals, V. C. Farmer, Ed. (Mineralogical Society, Lon-

The past decade has seen a significant expansion both in the interpretive methodologies used to extract mineralogical information from asteroid spectra and other remote-sensing data and in the number of asteroids for which mineralogical characterizations exist. Robust mineralogical characterizations now exist for more than 40 asteroids, an order a magnitude increase since Asteroids II was publi...

As announced in the Amer. M'inerol. 55, 1080 (1970) the summer meeting of the A.C.A. included a Special Session on Mineralogical Crystallography. Fifteen papers were given in a full-day session; abstracts are printed below. In a brief discussion at the end of the day the participants, who included the presidents of the A.C.A., M.A.C., and M.S.A., voted unanimously that the Session on Mineralogi...

If life ever existed, or still exists, on Mars, its record is likely to be found in minerals formed by, or in association with, microorganisms. An important concept regarding interpretation of the mineralogical record for evidence of life is that, broadly defined, life perturbs disequilibria that arise due to kinetic barriers and can impart unexpected structure to an abiotic system. Many featur...