Most commodity prices fell Thursday after a U.S. Supreme Court ruling on health care and a European summit meeting heightened concerns about demand for basic materials.
The downturn was widespread and mirrored a decline in stocks.
The Supreme Court upheld most of President Barack Obama's health care overhaul, including a key requirement that nearly every American have health insurance by 2014.
Investors worried that the provisions could mean less disposable income for businesses and consumers when economic growth already is slower, said Phil Streible, a commodities broker at RJ O'Brien.
A new government estimate concluded the economy grew at an annual rate of 1.9 percent and consumer spending grew 2.5 percent during the January-March quarter, below the previous 2.7 percent estimate.
Investors also are skeptical that European leaders will agree on a way to deal with the region's crippling debt crisis during their meeting. The financial problems have hurt the economies of several countries in Europe and are affecting growth in other parts of the world.
Investors sold commodities and put money into the dollar and bonds.
Gold, which often is considered a safe haven, was hurt by a weaker euro, George Gero, a vice president at RBC Global Futures, wrote in an email.
Gold and other commodities are priced in dollars so they become more expensive for traders using other currencies when the dollar is stronger.
Gold for August delivery fell $28 to finish at $1,550.40 an ounce and July silver dropped 69.5 cents, or 2.6 percent, to $26.247 per ounce.
July copper decreased 2.35 cents to end at $3.326 per pound, July platinum fell $23.30 to $1,386.40 per ounce and September palladium ended down $15.85 at $563.90 per ounce.
In energy trading, natural gas prices dropped after the Energy Department said supplies grew more than expected last week. Natural gas ended down 7.6 cents at $2.722 per 1,000 cubic feet.
Benchmark oil fell $2.52 to end at $77.69 per barrel. Heating oil dropped 4.18 cents to $2.5519 per gallon and wholesale gasoline was essentially flat, decreasing 0.62 cent to $2.6142 per gallon.