Clarence King exposes the diamond hoax in Wyoming

Background. The diamond hoax of 1872 involved prospectors Philip Arnold and John Slack, who sold a non-existent American diamond deposit to prominent businessmen in San Francisco and New York City. In 1871, they traveled through Navajo territory, collecting chrome diopsides, pyrope garnets, and ilmenites. The swindle triggered a brief diamond prospecting craze in the western United States, including Arizona, New Mexico, Utah, Wyoming, and Colorado.

Investigation. Clarence King, an American geologist, mountaineer, and author, led the effort that uncovered the swindle. King and some of his crew tracked down the secret location in northwest Colorado and exposed it as a fraud, now known as the diamond hoax of 1872. The exposure ended the prospecting excitement the hoax had stirred across the western United States.

Official Revelation. A published official letter addressed November 11, 1872, to the Board of Directors of the San Francisco and New York Mining and Commercial Company is documented as stating that the new diamond fields were discovered to be a fraud. The surviving record is a twelve-page item published in San Francisco in 1872; the passages do not describe the circumstances of its delivery or its public reception.