An X‐ray determinative curve has been produced for the rapid analysis of simple silver halides. Complete analyses of thirty‐two specimens of silver halides and examination of approximately fifty more by X‐ray diffraction show that they are, with very few exceptions, embolites with only a few percent of silver iodide present. Most of these fall within a small composition field and it is possible that there has been more than one period of halide formation which would account for specimens outside this field. All the pure silver iodides gave hexagonal diffraction patterns except those containing small amounts of copper, suggesting an excess of iodide ions in the solutions at the time of formation.