UPDATE 1-U.S. Silica posts bigger-than-expected loss on weak demand, prices

(Adds forecast, compares with estimates)

Oct 29 (Reuters) - Frac sand miner U.S. Silica Holdings reported a bigger-than-expected loss for the third quarter on Tuesday, hit by low sand prices and softening demand as shale activity slowed.

Sand prices have been falling as shale producers are sourcing sand from local basins to save transportation costs rather than use the Northern White sand brought from Wisconsin.

Sand is used to open cracks in shale rocks to release oil and gas and is the most widely used proppant in fracking.

In the oil & gas segment, the company sold 3.9 million tons in the third quarter, down 1% from the prior quarter. For the fourth quarter, it expects volumes to fall 10% sequentially.

Price per ton was also hit by multiple new mines coming online in West Texas, worsening an already oversupplied market.

The company reported a net loss of $23 million, or 31 cents per share, for the quarter ended Sept. 30, compared with a profit of $6.3 million, or 8 cents per share, a year earlier.

Adjusted loss came in at 17 cents per share, well below analysts' average estimate of a loss of 3 cents, according to Refinitiv IBES data.

Revenue fell 14.5% to $361.8 million, missing estimates of $395.5 million. (Reporting by Shariq Khan and Taru Jain in Bengaluru; Editing by Vinay Dwivedi)