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.
Subscribe to 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.
Sign up for MoneyWeek's newsletters
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.
Matthew graduated from the University of Durham in 2004; he then gained an MSc, followed by a PhD at the London School of Economics.
He has previously written for a wide range of publications, including the Guardian and the Economist, and also helped to run a newsletter on terrorism. He has spent time at Lehman Brothers, Citigroup and the consultancy Lombard Street Research.
Matthew is the author of Superinvestors: Lessons from the greatest investors in history, published by Harriman House, which has been translated into several languages. His second book, Investing Explained: The Accessible Guide to Building an Investment Portfolio, is published by Kogan Page.
As senior writer, he writes the shares and politics & economics pages, as well as weekly Blowing It and Great Frauds in History columns He also writes a fortnightly reviews page and trading tips, as well as regular cover stories and multi-page investment focus features.
Follow Matthew on Twitter: @DrMatthewPartri
-
New Chase bonus deal takes savings rate to 4.75% – is it worth it?
Chase’s latest savings deal propels it into second place in the best-buy tables, but there are some pitfalls to look out for
By Katie Williams Published
-
Review: Trasierra – a yoga retreat in the Spanish hills
Flora Connell joins a yoga retreat at Trasierra, in the Sierra Morena mountains north of Seville
By Flora Connell Published
-
Why CEOs deserve a pay rise
Opinion The CEOs of big companies often come under fire for being grossly overpaid. But the truth, as per some economists, is the opposite. Do they merit a pay rise?
By Stuart Watkins Published
-
Rolls-Royce stock jumps 15% – could it climb further?
Aircraft-engine group Rolls-Royce’s CEO has been hailed as a hero for spearheading the firm’s recovery. And the future looks bright, says Matthew Partridge
By Dr Matthew Partridge Published
-
The power of private markets
Interview Helen Steers, co-manager of the Pantheon International investment trust, tells MoneyWeek about the vast array of compelling opportunities in private equity
By Andrew Van Sickle Published
-
Vertex Pharmaceuticals is an uncommon opportunity in rare diseases
Vertex Pharmaceuticals operates in a profitable subsector and is poised for further success
By Dr Mike Tubbs Published
-
Global investors have overlooked these top tips in emerging markets
Opinion Chris Tennant, co-portfolio manager of Fidelity Emerging Markets, picks three attractive companies in emerging markets
By Chris Tennant Published
-
King Coal has not been dethroned yet — should you buy?
The demand for coal is only growing, yet investors don’t seem to want to take advantage of the opportunity, says Rupert Hargreaves
By Rupert Hargreaves Published
-
It’s time to start buying Europe again, says Merryn Somerset Webb
Opinion Europe's stocks are cheap and the economic backdrop is starting to look cheerier, says Merryn Somerset Webb
By Merryn Somerset Webb Published
-
Prosus to buy Just Eat for €4.1 billion as takeaway boom fades
Food-delivery platform Just Eat has been gobbled up by a Dutch rival. Now there could be further consolidation in the sector
By Dr Matthew Partridge Published