SAN FRANCISCO -- Facebook CEO Mark Zuckerberg is definitely in the holiday-giving mood.

Late Tuesday, he donated 18 million of his shares in the social-networking company - worth nearly $500 million - to the nonprofit Silicon Valley Community Foundation, which works in education and health initiatives.

"I'm hopeful we'll be able to have as positive an impact in our next set of projects," Zuckerberg said in a status update on his Facebook page.

It is Zuckerberg's second big donation since he joined the Giving Pledge, the Bill Gates-Warren Buffett organization that has asked the wealthiest people in the U.S. to give to worthwhile causes.

His first centered on education reform with Startup: Education in Newark, N.J.

"I'm really proud of the work we've done there, helping leaders like Gov. Chris Christie and Mayor Cory Booker sign the most progressive teachers contract in our country, opening four new district high schools, 11 new charter schools and more," Zuckerberg wrote on his Facebook profile.

USA Today