The compositional variety, the range of color variation, and the diverse origin of tourmalines has led to several books on the subject. Some are very technical, either mineralogically or technically, but for me one stands out for the mineral collector. The Collector’s Guide to the Tourmaline Group by Robert J. Lauf (Schiffer Publishing) combines adequate detail on tourmaline chemistry and taxonomy with a pictorial account of all the recognized tourmaline species. Lauf does all this at a level that is not daunting for the non-geologist. The price is right also, $19.99 list for the oversize softcover book, and I found it for a few dollars less online.
Incidentally, this is one of a series of books published by Schiffer on various minerals or mineral groups. All are informative and affordable and well illustrated.