Occurrence of Claudetite in Imperial County, California

In the American Mineralogist, vol. 19, 1934, Professor Charles Palache describes the crystallography of claudetite, arsenic trioxide, from Imperial County, California, and the United Verde Mine, Arizona. The latter is a product of a mine fire and therefore specimens from the former locality constitute perhaps the best natural crystal occurrence recorded to date. Some claudetite was obtained as a natural oxidation product of arsenical pyrite ores in the San Domingo Mines of Portugal many years ago, but so far as the author is aware the quality of this material did not compare with the present natural occurrence.