Facebook couple Mark Zuckerberg and Priscilla Chan top list of US philanthropists

Mr Zuckerberg and Ms Chan topped the list of donors last year with their near-$1bn gift to the Silicon Valley Community Foundation (GETTY)

America’s biggest donors last year may have been the Facebook squillionaires Mark Zuckerberg and his wife Priscilla Chan, but it was the second most generous, George Mitchell, who was perhaps more noteworthy.

Not only because he died, aged 94, last July. But because his bequest was to research ways of reducing the environmental damage caused by fracking – the gas extraction technique that made him a billionaire.

Mr Mitchell is widely credited in the industry with being the first tycoon fully to commercialise hydraulic fracturing. But its critics say the chemicals used in the process can poison local water resources. When the Texan Mr Mitchell died, he left an estimated $750m to his family foundation.

Mr Mitchell and his wife established the fund in 1978, by which time he was already spectacularly wealthy. Brought up in relatively humble circumstances, his parents emigrated from Greece to the US where his father ran a shoeshine business. Mr Mitchell got a summer job in the Louisiana oil fields when he was a teenager, later going on to get a degree in petroleum engineering. He sold his exploration business in 2002 for $3bn.

Mr Zuckerberg and Ms Chan topped the list of donors last year with their near-$1bn gift to the Silicon Valley Community Foundation, which is keeping its counsel about what precisely it plans to spend it on. Their donation came in the form of 18 million shares of Facebook – matching the same number they gave in 2012. According to the Chronicle of Philanthropy’s top 50 list of US donors, Mr Zuckerberg has said the latest gift would focus on children. Ms Chan is a paediatrician.

In 2010, then 26, Mr Zuckerberg joined the Giving Pledge network of rich entrepreneurs who agreed to give at least half of their wealth to philanthropy. He said at the time: “People wait until late in their career to give back. But why wait when there is so much to be done?”

Despite his example, other young billionaires were notably absent on the list. The median age of donors was 72.5.

In third place came the Nike sportswear founder Phil Knight and his wife, who gave $500m to cancer research at a foundation in their native Oregon.

However, that comes with a stretching proviso – the Oregon Health & Science University Foundation has to match the gift in two years or lose it.