Stock markets ended a turbulent quarter on a sour note on Friday, with shares falling sharply amid investors' growing despair about political efforts to deal with the monumental challenges facing the world economy.

The Dow Jones Industrial Average dropped 2.16% on Friday, ending the quarter down 12%—its worst percentage decline since the first quarter of 2009. Stocks in Europe and Asia also fell.

The selloff capped a dismal quarter marked by anxiety about the European sovereign-debt crisis, a U.S. economy flirting with a double-dip recession, and signs that hitherto fast-growing economies such as China are slowing down. Even some famed safe havens failed to perform—gold tumbled toward the end of the quarter, and the Swiss franc also dropped.

"I'd like to forget all about it," said Randy Frederick, director of trading and derivatives at Charles Schwab in Austin, Texas. "It was an ugly quarter, and it started right after the quarter began. There was a whole string of things. When the market might have wanted to go higher, something always seemed to come along to squash it."

The onslaught of bad news, coupled with periodic flashes of optimism, led to one of the most volatile periods ever for stocks. On Friday, the Dow plunged 240.60 points to 10913.38, after big gains earlier in the week. That was the 18th time the Dow moved by more than 200 points in the quarter. In August, it swung by more than 400 points in four consecutive days.