* Mosaic, Potash Corp sink after Russia quits top potash cartel
* Occidental Petroleum profit misses forecast; stock falls 3.4 pct
* Sprint posts wider loss, but revenue rises; stock up 4 pct
* Dow off 0.2 pct, S&P 500 off 0.1 pct, Nasdaq up 0.3 pct
By Alison Griswold
NEW YORK, July 30 (Reuters) - The Dow and the S&P 500 edged lower on Tuesday, erasing earlier gains, after a selloff in materials and energy shares and a shakeup in the potash sector took a toll on the broader market.
Mosaic Co stock was among the biggest drags on the S&P 500, sinking 18.1 percent to $43.38 after Russia's Uralkali dismantled one of the world's largest potash partnerships by pulling out of a venture with its partner in Belarus, a move it expects will drive global prices down 25 percent.
Occidental Petroleum Corp shares tumbled more than 3 percent and helped pull down the S&P 500 after the company reported a smaller-than-expected quarterly profit, hurt by lower oil prices in the Middle East and North Africa.Its stock dropped 3.4 percent to $87.49.
Six of the benchmark S&P's 10 industry sector indexes declined, led by losses in telecommunications services. , materials and energy shares. The S&P telecom services index fell 1.5 percent, while the S&P materials index dropped 0.4 percent and the S&P energy index declined 0.2 percent.
"Usually in the summer months, things tend to be more volatile and markets tend to see less participation, so it's not uncommon to see big moves in the market without any specific news attached," said Michael James, managing director of equity trading at Wedbush Securities in Los Angeles.
Volume could be light in advance of the Wednesday statement from the Federal Reserve, which is expected at the end of a two-day policy meeting of the Federal Open Market Committee. Investors will scrutinize the statement for any additional hints of when the central bank may begin to pare its $85 billion a month in bond purchases.
The Dow Jones Industrial Average dropped 30.47 points, or 0.20 percent, to 15,491.50. The Standard & Poor's 500 Index fell 1.78 points, or 0.11 percent, to 1,683.55. The Nasdaq Composite Index added 11.89 points, or 0.33 percent, to 3,611.03.
Verizon had the greatest negative impact on the Dow and the S&P 500, sliding 2.2 percent to $50.36.
In more fallout from the potash sector, shares of Intrepid Potash sank 28.5 percent to $13.90. U.S-traded shares of Potash Corp fell 18.6 percent to $30.86. Agrium slid 5.2 percent to $86.69.
Shares of Pfizer, the largest U.S. drugmaker, rose 0.8 percent to $29.77 and helped support the S&P 500 after the company reported results. Pfizer's second-quarter earnings slightly exceeded estimates as the company lined up a business split that could lead to the spinoff of its generics division.
Goodyear Tire & Rubber stock rose 9.7 percent to $18.70 after setting a nearly five-year high of $19.60. The company reported that its quarterly profit more than doubled, and cited lower raw material costs and stabilizing sales in Europe as major reasons for its jump in profits.
In contrast, Coach Inc shares dropped 7.9 percent to $53.27 after the leather goods maker reported soft sales at its North American stores and announced the departures of two more executives. The stock was among the S&P 500's biggest percentage decliners.
Mobile service provider Sprint Corp posted a wider quarterly loss on costs from shutting down its Nextel network, but revenue grew as customers spent more on wireless services. Sprint's stock jumped 4 percent to $5.99.
With results in from 60 percent of S&P 500 companies, 67.4 percent have exceeded earnings expectations - in line with the average beat over the last four quarters. About 55 percent of companies have topped revenue expectations, more than the 48 percent of revenue beats in the past four earnings seasons but below the historical average, Thomson Reuters data showed.