Colusite was named by Mr. Reno H. Sales, Chief Geologist of the Anaconda Copper Mining Company, a number of years before the mineral was studied in detail by Landon and Mogilnor (1933), and by Zachariasen (1933). Somewhat earlier Schneiderhöhn and Ramdohr (1931) had referred the mineral to the tetrahedrite group, but without evidence. We have re-examined the mineral in this laboratory using well-authenticated material labelled colusite, which was collected a number of years ago by geologists associated with the Anaconda Company. A re-examination of the paragenesis of colusite has been undertaken by Nelson (p. 369, this journal) of the Montana School of Mines, in cooperation with the Anaconda Copper Mining Company staff. Our manuscript was submitted to Mr. Nelson whose independent check of our results is contained in his paper.