What was the name of the 1872 Colorado fraud in which a fake diamond field was promoted?

The 1872 Colorado fraud involving a promoted fake diamond field was called the Great Diamond Hoax.

Philip Arnold and JohnSlack secretly acquired several hundred dollars’ worth of uncut diamonds and other gemstones. They then salted a remote area in northwestern Colorado, planting the stones in the soil so investors could “discover” them. Arnold persuaded a cousin, John Slack, to help present the scheme as a genuine strike.

The pair took samples to a San Francisco bank, where banker William C. Ralston and other investors became interested. Ralston brought in experienced New York jeweler Charles Lewis Tiffany, whose experts inspected the stones but did not initially recognize the deception. Investors bought the supposed field for a large sum in 1872.

The fraud unraveled when geologist Henry Janin examined the site and found the stones scattered unnaturally. The episode is often confused with genuine Colorado mineral discoveries, including the Cripple Creek gold rush, which began decades later. Arnold escaped with much of the money, while Slack received a smaller share.