Refinement of an Amesite-2H₁ Polytype from Postmasburg, South Africa

Hong Zheng and Sturges W. Bailey 301

Interaction of Vermiculite with Aliphatic Amides (Formamide, Acetamide and Propionamide): Formation and Study of Interstratified Phases in the Transformation of Mg- to NH₄- Vermiculite

Antonio Ruiz-Conde, Antonio Ruiz-Amil, Jose L. Perez-Rodriguez, Pedro J. Sanchez-Soto and Francisco Aragon de la Cruz 311

Comparison of the Mineralogical and Chemical Composition of 2 Shales from the Western Canada Sedimentary Basin and the United States Gulf Coast

Patrice de Caritat, John Bloch, Ian Hutcheon, Fred J. Longstaffe and Hugh J. Abercrombie 327

Sorption of Atrazine by Al- and Ca-Saturated Smectite

B. L. Sawhney and S. S. Singh 333

The Chemical Composition of Serpentine/Chlorite in the Tuscaloosa Formation, United States Gulf Coast: EDX vs. XRD Determinations, Implications for Mineralogic Reactions and the Origin of Anatase

P. C. Ryan and R. C. Reynolds, Jr. 339

Phosphates in Some Missouri Refractory Clays

Robert B. Hall, Eugene E. Foord, David J. Keller and Walter D. Keller 353

Motoharu Kawano and Katsutoshi Tomita 365

Textural Transition and Genetic Relationship between Precursor Stevensite and Sepiolite in Lacustrine Sediments (Jbel Rhassoul, Morocco)

Azeddine Chahi, Bertrand Fritz, Joelle Duplay, Francis Weber and Jacques Lucas 378

Illite-Smectite Alteration and Accompanying Reactions in a Pennsylvanian Underclay Studied by TEM

F. Elsass, J. Srodon and M. Robert 390

Crystallographic Controls on the Alteration of Microcline Perthites from the Spruce Pine District, North Carolina

Julia M. Sheets and Rodney T. Tettenhorst 404

Quantitative Phase Analysis of Bidi-Koum Bauxites (Guinea)

Frank Feret, Monique Authier-Martin and István Sajó 418

Characterization of Iron-Manganese Concretions in Kentucky Alfisols with Perched Water Tables

Min Zhang and A. D. Karathanasis 428

Analytical Electron Microscopic Study of the Noncrystalline Products Formed at Early Weathering Stages of Volcanic Glass

Motoharu Kawano, Katsutoshi Tomita and Yasushi Shinohara 440

Surface Structural Model for Ferrihydrite

A. Manceau and W. P. Gates 448

XRD Measurement of Mean Crystallite Thickness of Illite and Illite/Smectite: Reappraisal of the Kubler Index and the Scherrer Equation

Victor Drits, Jan Srodon and D. D. Eberl 461

Reduction and Reoxidation of Nontronite: The Data Reassessed

L. Heller-Kallai 476

A Warning on the Use of Mössbauer Spectroscopy in Semiquantitative Analysis of Soils

Celia Saragovi and Ana Mijovilovich 480

Enhanced Second-Order Optical Nonlinearity of Dye Molecules Adsorbed onto Laponite Particles

Carlo Boutton, Martti Kauranen, André Persoons, Michael P. Keung, Katrien Y. Jacobs and Robert A. Schoonheydt 483

The Effect of Chemical Pretreatments on the Composition of Natural Illite

Philip E. Rosenberg and Robert L. Hooper 486