U.S. stocks headed toward a weekly loss Friday as they followed world markets into the red. Meanwhile, global commodity prices continued their downward spiral. With no clear trend emerging from U.S. corporate earnings results and disappointing U.S. home sales data released Friday, all three U.S. markets were down in midday trading.

“What we’re seeing right now in this earnings season is a mixed bag,” said Adam Sarhan, CEO of Sarhan Capital, an investment and advisory firm. “Companies are beating estimates but those estimates have been ratcheted down for several months.”

Energy and basic material stocks were leading the sell-offs Friday, while tech and telecom shares were showing gains by midday. Amazon.com Inc. (Nasdaq:AMZN) shares continued their rally after the online seller and cloud-storage services provider reported a surprise quarterly profit. The company's stock gained more than 15 percent to $556.45 by midday.

The Dow Jones Industrial Average (INDEXDJX:.DJI) dropped 71.82 points, or 0.41 percent, to 17,660.10. The Standard & Poor's 500 index (INDEXSP:.INX) dipped 7.40 points, or 0.35 percent, to 2,094.84. And the Nasdaq composite (INDEXNASDAQ:.IXIC) lost 2.98 points, or 0.06 percent, to 5,142.93.

European and Asian stocks closed in the red Friday after a sell-off in global commodities that could indicate a major global slowdown is underway. Copper prices fell to their lowest level since 2009 and mining stocks retreated after Anglo American plc (LON:AAL), a leading mining company, reported a 36 percent drop in earnings and said it was slashing 6,000 jobs. Anglo American CEO Mark Cutifani said volatility and global economic uncertainly would continue to impact global mining, a signal of an economic slowdown in construction and other key industrial activities.

“Except for cocoa and cattle, all commodity prices are down. Demand remains very weak and that doesn’t bode well for the global economy,” said Sarhan. “We have lackluster growth across the global economy with central banks either printing money or offering easy money.”

The U.S. Commerce Department said Friday that new home sales dropped to their lowest level in seven months while May sales were revised lower, indicating a setback in housing market recovery. New home sales dropped 6.8 percent to a seasonally adjusted annualized rate of 482,000. May sales were revised from 546,000 to 517,000.

On the upside, preliminary monthly data from Markit Economics about business purchases ticked up to 53.8 in July, from a 20-month-low in June of 53.6. Readings above 50 indicate growth. A strong dollar was putting pressure on U.S. exports, according to the respondents to the monthly survey.

The U.S. dollar strengthened against key Asian-Pacific currencies hit by the commodities row and China’s announcement on Friday it would allow the yuan to fluctuate more freely in an effort to weaken it to boost exports. A weaker yuan would gut exports from other Asian emerging markets. Australia’s dollar is being hit by weak demand for its core mining exports.

Since Thursday, four major U.S. air carriers have reported lower than expected revenue for their second quarters. Airline stocks dipped, as American Airlines Group Inc (Nasdaq:AAL) shares fell 2.06 percent to $41.76 while Spirit Airlines Incorporated (Nasdaq:SAVE) stock dropped 1.89 percent to $60.21 following the carriers release of their quarterly earnings statements before markets opened on Friday.

United Continental Holdings Inc (NYSE:UAL) stock was recovering from Thursday’s sell-off after the airline reported a miss on revenue in its second quarter. United’s stock recovered from Thursday’s decline, gaining 2.15 percent to $57.89 on Friday morning.

Southwest Airlines Co. (NYSE:LUV) shares were down 1.04 percent to $36.11 after shedding nearly 3 percent on Thursday. Southwest’s price was still above its Wednesday close as investors saw only a slight revenue miss and viewed the airline's plans to expand to 50 international destinations as good news for the budget carrier.