* TSX falls 91.78 points, or 0.72 percent, at 12,702.66 * All 10 major sectors decline * Potash slips 2 percent on results By John Tilak TORONTO, Jan 31 (Reuters) - Canada's main stock index hit a two-week low on Thursday, weighed down by Potash Corp after weak fourth-quarter results and by other resource stocks, which slipped along with commodity prices as investors worried about global growth. Potash, the world's biggest fertilizer company, reported a surprisingly large drop in fourth-quarter profit and gave a first-quarter outlook below Wall Street's forecast. The stock declined 2 percent. Research In Motion Ltd shares dived yet again, falling 8.3 percent to C$12.71, the day after the BlackBerry maker released a new line of phones, as its release dates disappointed. Investors also tried to digest data from Europe, which included a drop in German retail sales, stagnant French consumer spending and a huge quarterly loss at Deutsche Bank. But a measure of business activity in the U.S. Midwest rose in January to its strongest since April. Oil prices dipped below $115 a barrel and gold prices fell nearly 1 percent, weighing on the resource-heavy Toronto index. "The nature of resources is they respond to commodity prices both current and anticipated. They tend to be more volatile reflecting that," said Bob Gorman, chief portfolio strategist at TD Waterhouse. Gorman said he wouldn't be surprised to see the market pull back after the strong run it's had over the past several weeks. The Toronto Stock Exchange's S&P/TSX composite index was down 91.78 points, or 0.72 percent, at 12,702.66. The index fell to 12,701.92, its lowest since Jan. 18. All 10 major sectors on the index were in the red. The materials sector, which includes mining stocks, gave back 1.1 percent. Goldcorp Inc was down 1.5 percent at C$35.47. The energy sector dropped 0.6 percent, with Canadian Natural Resources Ltd falling 2.4 percent to C$30.43 and playing one of the biggest roles in leading the market lower. Financials, the index's weightiest sector, were down 0.6 percent. Royal Bank of Canada fell 0.5 percent to C$62.29, and Bank of Nova Scotia lost 0.8 percent to C$58.43.