Dr. George Tunell of the Geophysical Laboratory has kindly brought to my attention the fact that incorrectly identified material was used in securing the x-ray data erroneously called antlerite in my paper entitled “Identification of the copper ore minerals by means of x-ray powder diffraction patterns”; this Journal, August issue, 1935. By means of optical methods I have checked the supposed antlerite that I used, and find it to be brochantite. I also find that the data obtained from this specimen of brochantite check the original data of Posnjak and Tunell (Am. Jour. Sci., vol. 18, pp. 12–24, 1929) better than the brochantite record published in my article cited above. For purposes of comparison I am listing the three records for brochantite in Table 1.