Cosalá

Its exact composition resisted settlement for over a century because lead and bismuth are almost indistinguishable to X-rays.

Cosalite is named for the Cosala silver district in Sinaloa, Mexico, where Frederick Augustus Genth described it in 1868 in Contributions to Mineralogy No. VII, in the American Journal of Science and Arts. Srikrishnan and Nowacki redetermined the structure in 1974, and Wulf showed in 1995 how to tell lead from bismuth experimentally in these sulfosalts, since the two elements sit next to each other in the periodic table. It also occurs in Japan, at the Hagidaira mine in Gunma Prefecture.