July slaughter sends commodities to 13-year low

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The downward slide in commodity prices is accelerating, surpassing the low reached during the financial crisis in 2008 and reaching a 13-year low.

"This is one of the worst months in history for commodities," said Jodie Gunzberg, global head of commodities at S&P Dow Jones Indices.

The S&P GSCI index, a measure of a basket of 24 commodities, lost 14 percent of its value this month, with nearly every single component trading in negative territory.

Indeed, the magnitude of the losses is shaping up to be the seventh worst in 45 years, data from S&P Dow Jones Indices show.

Gunzberg said it's rare for all commodities to go down at once because energy, metals and agricultural goods are generally not correlated to each other.