27 April 1990
Vol 248, Issue 4954

About The Cover

Pseudocolor transmission electron micrograph of fibrous, lath-shaped, diagenetic illite (less than 0.1-micrometer-size fraction) from the Repetto Formation, Santa Barbara Channel, California. Analysis of the sizes of illites and other clay minerals indicates that they coarsen by a process known as Ostwald ripening. See page 474. [Photo by Reed Glasmann, Unocal Corporation]