(FILES)Facebook Founder and CEO Mark Zuckerberg speaks during an interview session with The Atlantic at the Newseum in Washington, DC, in this September 18, 2013 file photo. Zuckerberg will sell 41.35 million 'B' shares in the company, worth about $2.3 billion, for tax purposes, a filing with US stock market regulators said December 19, 2013. These shares will allow Zuckerberg to retain power over Facebook because each has 10 voting rights. Proceeds from the sale will allow the young billionaire to pay taxes due on the exercise of an option enabling him to obtain 60 million additional 'B' Facebook shares. (JIM WATSON/AFP/Getty Images) 
 
 Facebook's Mark Zuckerberg is donating another $1 billion worth of stock to the Silicon Valley Community Foundation, in the latest installment of the 29-year-old Internet mogul's pledge to spend more than half his wealth on philanthropy. 
 
 The donation is "by far the largest gift in our history," said Emmett Carson, CEO of the Mountain View-based foundation, which will help Zuckerberg allocate the donated assets in coming years. Carson declined to say how the money will be used, but added: "We believe this gift will immensely improve the lives of people here and elsewhere." 
 
 Facebook announced the gift while disclosing plans for a sizable stock offering in which the company will raise almost $1.5 billion in cash, taking advantage of the stock's current high trading price by selling 27 million new shares. Zuckerberg is also selling about $2.3 billion worth of his own shares, which the company said he'll use to cover taxes he'll owe after exercising an option to buy more Facebook stock. 
 
 When the dust settles, the youthful CEO will have reduced his stake in the high-flying social networking company -- but only slightly. Zuckerberg will control about 62.8 percent of voting power wielded by Facebook shareholders, down from 65.2 percent. He will still own about 444.2 million shares, which were worth more than $24 billion on Thursday. 
 
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 Zuckerberg has made headline-grabbing gifts to charitable works before. He gave a similar-sized block of stock to the foundation last year, although the shares were worth only about $500 million at the time, because Wall Street was less enthusiastic about the company then. The value of that donation has more than doubled, as Facebook's booming advertising business has caused its stock to soar. 
 
 Along with receiving donations and making direct grants to charities, the community foundation advises a number of wealthy individuals on philanthropic giving. It offers a variety of custom services, such as administering charitable funds on an individual's behalf. 
 
 As part of its work with Zuckerberg, the foundation helped oversee his pledge of $100 million to improve public schools in Newark, N.J., which he announced in 2010. It also channeled his contribution to the multi-million-dollar series of "Breakthrough Prize" awards for math and science research, which Zuckerberg has funded jointly with other tech luminaries including Sergey Brin, Yuri Milner and Jack Ma. 
 
 Zuckerberg signed on three years ago to the "Giving Pledge" campaign, promoted by billionaires Bill Gates and Warren Buffett, in which wealthy individuals vow to give at least half their assets to philanthropy over the course of their lives. 
 
 The Facebook CEO and his wife, pediatrician Priscilla Chan, have said they are interested in causes related to education and health. Zuckerberg has avoided discussing their charitable goals in detail, however. Carson declined to answer questions about how the foundation will manage or distribute the donated stock. 
 
 Facebook, meanwhile, said it has no specific plans for the money raised from its new stock offering, which will be the company's first since its trouble-plagued initial public offering in May 2012. Facebook is already flush with cash; it ended the last quarter with more than $9 billion on hand. 
 
 But there have been reports Facebook recently offered to pay an astonishing $3 billion to buy the messaging service Snapchat, which has become a popular rival for younger Internet users' attention. While the offer was rebuffed, word of the new stock offering prompted speculation Facebook may have other big acquisitions in mind. 
 
 Facebook's stock has surged over the last year, as the company overcame early criticism that it was slow to catch on to the growing popularity of smartphones and tablets. At the time of its IPO, Facebook had no way of selling advertising for the smaller screens of mobile devices. 
 
 But it has subsequently built a thriving mobile ad business, which will bring the company $3 billion in revenue this year, according to eMarketer. The research firm projects those sales will help make Facebook the second-biggest seller of online advertising in the United States, behind only Google (GOOG). Facebook shares closed Thursday at $55.05. 
 
 In a related move, Facebook said Zuckerberg will exercise a long-standing option to buy 60 million new shares, at a price that is likely much lower than the public trading price. He will sell 41.35 million shares, primarily to cover tax obligations, and donate 18 million shares. 
 
 Venture capitalist Marc Andreessen, an early Facebook investor, will also sell 1.6 million shares, worth about $87 million. 
 
 Contact Brandon Bailey at 408-920-5022; follow him at Twitter.com/BrandonBailey ||||| wealth Facebook CEO Zuckerberg expects staggering tax payments Dec. 19, 2013 at 3:24 PM ET 
 
 ROBERT GALBRAITH / Reuters 
 
 Last year Mark Zuckerberg paid an estimated $1 billion in taxes, which was considered one of the biggest payments ever. 
 
 Until now. 
 
 According to company filings, the Facebook chief executive officer is selling 41.4 million shares of Facebook worth around $2.3 billion. The company said "most" of the net proceeds will go to pay taxes, which means that over a two-year period, Zuckerberg may be paying between $2 billion and $3 billion in federal and state taxes. 
 
 A $2 billion payment this year would be around 4 percent of the total income taxes that were collected in California in 2012. 
 
 
 
 It's hard to say whether his tax bill is the biggest this year — or ever — because the IRS doesn't rank the top taxpayers. And while Forbes, Bloomberg and others track the wealth gains of the rich, no one tracks the top taxpayers among the rich. 
 
 The IRS does crunch data on the top 400 earners each year. For 2009, the most recent period available, the top 400 earners paid a total of $16 billion in taxes, with an average tax bill of $40 million each. 
 
 Zuckerberg's tax bill could be more than 50 times that amount. 
 
 Of course, his tax bill is so high because his income (at least on paper) is even more massive. And with a net worth of more than $27 billion, according to the Bloomberg Billionaires Index, it won't exactly cramp his lifestyle. What's more, Zuckerberg has charitable deductions and trust structures that help reduce his effective tax rate. 
 
 But Zuckerberg is an extreme example of a dangerous phenomenon: the stock sales of the wealthy account for an outsized share of America's income taxes. And that dependence is growing with a rising stock market and a growing income gap. 
 
 
 
 In California, the top 1 percent pay more than 40 percent of the state's income taxes. The stock-selling, super rich like Zuckerberg account for a large share of that 40 percent. 
 
 Facebook's initial public offering was so important to the state government's tax collections that it had to lower its budget projections by more than $600 million because of the company's weak IPO. Now that Facebook's shares are soaring, the budget probably needs to be updated with higher revenue numbers. 
 
 For now, Washington and Sacramento are cheering the soaring stock market, and sellers like Zuckerberg. They won't be as happy when the trend reverses. 
 
 
 
 —By CNBC's Robert Frank. Follow him on Twitter @robtfrank. 
 
 Related stories: 
 
 Zuckerberg to sell $2.3 billion worth of Facebook shares 
 
 Just how fast are the rich becoming richer? 
 
 Buffett's wealth: Up $37 million a day 
 
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– It may be true that people are a bit more generous around the holidays, but Mark Zuckerberg is taking that to a whole new level. Facebook's founder is once again making a hefty donation to the Silicon Valley Community Foundation: a block of Facebook stock worth $1 billion. He gave the foundation roughly the same amount of stock last year, but it was worth only half as much at the time. It's "by far the largest gift in our history," the foundation's CEO told the San Jose Mercury News, without providing any specifics on how the donation will be used. But it won't be the only stock to soon escape Zuckerberg's hands. CNBC reports he's selling off 41.4 million Facebook shares worth $2.3 billion ... to pay his taxes. Last year Zuckerberg's tax bill rang in at $1 billion, but this year's tab could be closer to $2 billion, an astounding sum considering that the top 400 earners in 2009 paid a total of $16 billion. Still, even after the tax man takes his due, Zuckerberg will have plenty of cash left to roll around in. He'll still have 444.2 million Facebook shares, worth around $24 billion, which give him about 62.8% of the voting power of Facebook shareholders, down from 65.2% before the sale and donation.