Volume 1A is the second of a series of revisions that the authors are preparing from their original five-volume work on rock-forming minerals, which is a standard reference for petrologists and mineralogists. Revision of the original series is necessary because of the explosion of the mineralogical literature, particularly in the specialities of microprobe chemical analysis, electron microscopy, intercrystalline and intracrystalline element distributions, mineral physics and thermodynamics, and phase equilibria. Many of these fields or techniques were only in their infacy when the first edition was prepared 20 years ago. The increase in the published literature has been so great that volume 1A requires 5 times as many pages to deal with one half of the mineral species covered in volume 1 of the first edition. For example, mullite, which was only mentioned briefly in the sillimanite section of the original edition, is now allotted its own 17-page section. Clearly, this second edition supplants the first with regard to scope and quantity of material covered.