Great frauds in history: Philip Arnold’s big diamond hoax
Philip Arnold and his cousin John Slack lured investors into their mining company by claiming to have discovered large deposit of diamonds. There were no diamonds.
Philip Arnold was born in Elizabethtown, Kentucky in 1829. After serving as a soldier in the Mexican-American War (which saw the US take over California), he became a gold prospector and was successful enough to return to Kentucky and buy a farm. By 1870 he was back in California and working as a prospector when he claimed to have discovered, along with his cousin John Slack, a large deposit of diamonds. This attracted the attention of several wealthy investors, including the founder of the Bank of California.
What was the scam?
Arnold and Slack’s “discovery” was the result of their buying diamonds and mixing them in with their samples. On this basis they attracted money from investors and used it to buy additional diamonds, which they then claimed were part of the original discovery. Having hooked the investors, Arnold and Slack then led them to their “mine” in Colorado, taking care to seed the ground with diamonds beforehand. Arnold and Slack then sold the mine, bringing the total amount they had received to $660,000 ($14.3m in today’s money).
What happened next?
The new owners set up the San Francisco and New York Mining and Commercial Company in 1872, raising $850,000 ($18.4m) from investors for 20% of the company, valuing it at $4.25m ($86.4m) and setting off a mini-boom in mining shares. However, US government geologist Clarence King, who had been surveying the area and was worried that his team had missed such a massive deposit, investigated and quickly concluded that it had been salted. By November 1872 the find was publicly revealed to be a fraud, though not before hundreds of prospectors had set off to Colorado.
MoneyWeek
Subscribe to MoneyWeek today and get your first six magazine issues absolutely FREE
Sign up to Money Morning
Don't miss the latest investment and personal finances news, market analysis, plus money-saving tips with our free twice-daily newsletter
Don't miss the latest investment and personal finances news, market analysis, plus money-saving tips with our free twice-daily newsletter
Lessons for investors
Arnold agreed to return $150,000 ($3.2m) in return for all charges being dropped, but managed to retire with the rest of his ill-gotten gains. Shareholders were left with shares in a worthless mine, though some received partial compensation. Later, one of the original investors admitted that if they had spent just an extra hour exploring the area, they would have spotted the scam – a lesson on the need for proper due diligence.
Get the latest financial news, insights and expert analysis from our award-winning MoneyWeek team, to help you understand what really matters when it comes to your finances.

-
Undervalued Asian stocks that can be the “winners of tomorrow”Opinion Nitin Bajaj, portfolio manager of Fidelity Asian Values Trust, highlights three investment opportunities across Asia
-
How dinosaur fossils became collectables for the mega-richDinosaur fossils are prized like blue-chip artworks and are even accelerating past the prices of many Old Masters paintings, says Chris Carter
-
How dinosaur fossils became collectables for the mega-richDinosaur fossils are prized like blue-chip artworks and are even accelerating past the prices of many Old Masters paintings, says Chris Carter
-
The battle of the bond markets and public financesAn obsessive focus on short-term fiscal prudence is likely to create even greater risks in a few years, says Cris Sholto Heaton
-
STS Global Income & Growth: Buying quality at a discountInvestors should consider STS Global Income & Growth to diversify away from mega-cap tech
-
'We still live in Alan Greenspan’s shadow'When MoneyWeek launched 25 years ago, Alan Greenspan was chairman of the Federal Reserve. We’re still living with the consequences of the whirlwind he sowed
-
Venture capital trusts that offer growth, income and tax reliefOpinion Alex Davies, founder of high-net-worth investment service Wealth Club, picks three venture capital trusts where he'd put his money
-
Go for growth: how to invest in emerging marketsDeveloping countries offer investors compelling long-term economic prospects, says David Prosser
-
How to invest in private equityNew forms of private equity funds give access to ordinary investors of more modest means. Should they rush in?
-
Isaac Newton's golden legacy – how the English polymath created the gold standard by accidentIsaac Newton brought about a new global economic era by accident, says Dominic Frisby