Volume 13 of Reviews in Mineralogy presents much of our present-day knowledge of micas. Since 1984 was too much material available to attempt to cover all of the hydrous phyllosilicates in one volume, the micas were treated first because of their abundance in nature and the fact that many detailed studies had been carried out on them. The serpentines, kaolins, smectites, chlorites, etc. would have to wait their turn. Now, four years later, that tum has come. Hence the peculiar nature of the title of this volume.

We know less about the rest of the phyllosilicates than we do about the micas, primarily because many of them are of finer grain sizes and lower crystallinities than most of the micas. As a result, we have been unable to determine as much detail regarding their structures, crystal chemistries, and origins. One compensating factor that has helped greatly in the accumulation of knowledge about these minerals is that some of them occur in large deposits that are of great economic value and thus stimulate interest. For this reason considerable emphasis in this volume will be related to the occurrence, origin, and petrology of the minerals.