John Slack

John Slack and his cousin, Philip Arnold, were prospectors and swindlers who perpetrated "The diamond hoax of 1872". They sold a false American diamond deposit to prominent businessmen in San Francisco and New York. It also triggered a brief diamond prospecting craze in the western USA, in Arizona, New Mexico, Utah, Wyoming, and Colorado.

John Slack, who had sold out early in the scheme to his cousin Phil Arnold, dropped from public view. He moved to St. Louis, where he owned a casket-making company. He later became a casket maker and undertaker in White Oaks, New Mexico, where he lived quietly and died in 1896 at the age of 76.

https://en.wikipedia.org/wiki/Diamond_hoax_of_1872

http://www.miningswindles.com/html/diamonds.html