Investors turned to precious metals amid another big selloff in the stock market Friday, boosting exchange-traded funds tracking gold and silver.

The September gold contract added $8.80 to $672.80, while silver gained 16 cents to $12.87.

The PowerShares DB Silver ( DBS) was adding 50 cents, or 2%, to $25.38. The PowerShares DB Precious Metals ( DBP) was gaining 46 cents, or 1.8%, to $26.21. The streetTracks Gold Shares ( GLD) was gaining $1.04, or 1.6%, to $66.50. The iShares Comex Gold Trust ( IAU) ascended $1.13, or 1.7%, to $66.64.

Real estate-related funds were among the hardest hit, as concerns about tightening credit and the burgeoning subprime mortgage crisis continued to escalate among investors. Major homebuilders including Lennar ( LEN), DR Horton ( DHI), Pulte Homes ( PHM) and Toll Brothers ( TOL) were all losing more than 2%.

The Ultra Real Estate ProShares ( URE) sank $2.47, or 5.4%, to $43.19. The iShares Dow Jones US Home Construction ( ITB) was losing $1.09, or 3.8%, to $27.63. The iShares FTSE NAREIT Mortgage REITs ( REM) was falling $1.05, or 3.2%, to $31.60.

ETFs tracking the European markets were also hit hard, as investors became increasingly concerned about the spread of U.S. credit worries across the Atlantic. A day after French bank BNP Paribas said it has suspended three of its funds with exposure to securities backed by U.S. subprime mortgages, Paris' CAC 40 sank 176.15 points and London's FTSE 100 closed down 232.90 points.

The PowerShares Dynamic Europe ( PEH) was sinking $1.06, or 4.4%, to $23.19. The iShares MSCI France Index ( EWQ) was losing $1.53, or 4.1%, to $35.39.

On the positive side, rising natural gas prices boosted some energy ETFs. The front-month natural gas futures contract was gaining 26 cents to $6.84.

The United States Natural Gas ( UNG) ETF was rising $1.58, or 3.8%, to $43.32. The PowerShares Dynamic Energy Exploration & Production ( PXE) was up 41 cents, or 2%, to $21.11. The PowerShares Dynamic Oil & Gas Services ( PXJ) was adding 28 cents, or 1.1%, to $24.89.

Rising semiconductor names boosted some bundled securities tacking technology. Atmel ( ATML) and On Semiconductor ( ONNN) were both adding more than 5%.

PowerShares Dynamic Technology ( PTF) was rising 57 cents, or 2.2%, to $26.39. The Internet Infrastructure HOLDRs ( IIH) was adding 7 cents, or 1.5%, to $4.70.

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