To write an introductorytext coveringthe entire field of mineralogy, including crystallography, petrology, and ore deposits, may seem presumptuous to many today. The fact that the author has taught this subject regularly through lectures and Iaboratories for 22 years is not in itself sufficient reason in his view. The motivation to do so arose out of the necessity to provide for students of this science and sister sciences 80 single useful and comprehensive book. Previous texts have been designed with subjects selected to conform to the courses taught at German Universities. It is questionable whether this limitation is still or ever was fortunate. Boundaries between the natural sciences have developed histori cally and should be maintained, in my opinion, only 80Spracticality dictates, such 80S in teaching. Each science is so intimately linked with its sister science that boundaries tend to disappear. It is known that interdisciplinary approaches frequently promote particularly successful research. Thus, also in the field of mineralogy, the influence of the allied sciences has been of great importance. This is particularly true of the influence of mathematics and physics on crystaIlo graphy and of geology on petrology. The changing emphasis on the one or the other branches of our science, however, has not always been beneficiaI. For example, it has resulted in judgments such 80S the following, attributed to the renowned mineralogist A. G. WERNER, relative to HAÜY, one of the founders of crystallography. The far-sighted geologist L.