Polished sections are ordinarily made of mineral aggregates. The orientation of a crystal under observation cannot be easily or accurately determined in such sections. In many instances information of great value could be obtained if polished sections of known orientation could be prepared. In a recent investigation1 it was found necessary to prepare polished sections of tiny arsenopyrite crystals (from one to a few millimeters in diameter) in such a way that the plane of the section might have any predetermined orientation. For this purpose a simple instrument and technique were developed which gave excellent results. Undoubtedly many crystallographic problems may be solved by the use of oriented polished sections, so the technique of preparing them is here-with described.