『In the early years of the development of mineralogy as a science, from about 1750 to 1850, many systems of classification were proposed, some based on chemical criteria, others on physical criteria. Of the former, a system originally devised by the Swedish chemist Berzelius gradually became generally accepted. This system groups the mineral species into major divisions, or classes, according to the nature of the anionic group present. As adapted for this book, these classes are as follows:
　�T．Native elements
　�U．Sulfides (including sulfosalts)
　�V．Oxides and hydroxides
　�W．Halides
　�X．Carbonates, nitrates, borates, iodates
　�Y．Sulfates, chromates, molybdates, tungstates
　�Z．Phosphates, arsenates, vanadates
　�[．Silicates』