Commodity prices tumbled on Tuesday, as a resurgent dollar and concerns about weakness in China’s economy pushed investors out of everything from crude oil to copper and corn. The S&P GSCI index, which tracks prices of 24 commodities, recorded its biggest one-day drop in more than a month and ended at its lowest since April 28. Before that, commodities markets, led by a recent rebound in crude oil, staged a surprising two-month rally that had pushed the index to its highs for the year. Driving the gains was a faltering greenback, which many short-term investors took as a signal to scoop up raw materials. But the dollar has abruptly reversed course in the past two days, […]