U.S. stock exchange traded funds (ETFs) were higher Tuesday but Microsoft (NasdaqGS: MSFT) shares were down over 1% after the tech giant said it will acquire Internet telephone services provider Skype for $8.5 billion in cash.

PowerShares QQQ (NasdaqGM: QQQ) was up 0.4% in midday trading Tuesday.  [Nasdaq ETF Higher as Microsoft Deal, Hearings in Focus]

Activity in the largest exchange traded fund for silver has spiked the past two weeks along with volatility as traders look for alternate ways to play the precious metal following a series of futures margin hikes. Daily trading volume in the $13 billion iShares Silver Trust (NYSEArca: SLV) has been running nearly ten times the average seen over the past six to nine months. [Silver ETF Volume Explodes on Margin Hikes, Volatility]

A rare earths exchange traded fund could see trading volume ramp up this week after Molycorp (NYSE: MCP) reports quarterly results following Tuesday’s closing bell. Molycorp is the third-largest holding in Market Vectors Rare Earth/Strategic Metals ETF (NYSEArca: REMX) at nearly 7% of the portfolio. The Van Eck ETF has about $500 million in assets and levies a net expense ratio of 0.57%. The fund is up nearly 13% so far this year as prices of rare earth materials have risen. [Molycorp Results to Steer Rare Earths ETF]

The largest oil exchange traded fund was down about 1% before Tuesday’s opening bell after CME Group announced higher margin requirements for oil futures. Oil prices bounced back somewhat Monday on fresh Middle East concerns, following last week’s big sell-off. Also, rising water levels in the Mississippi River threaten to inundate some of the largest oil refineries in the U.S. U.S. Gasoline Fund (NYSEArca: UGA) was up 6.3% on Monday, and U.S. Oil Fund (NYSEArca: USO) was up 5.1% but down 8.2% in the past two weeks. [Oil ETFs Lower After Margin Hike]

PowerShares has launched new low volatility and high beta exchange traded funds (ETFs) that help investors manage risk. PowerShares S&P 500 Low Volatility Portfolio (NYSEArca: SPLV) and the PowerShares S&P 500 High Beta Portfolio (NYSEArca: SPHB) just hit the market with the amount of volatility experienced and projected at low levels compared to recent years. [New Beta, Volatility ETFS from PowerShares]

Exchange traded funds that invest in clean energy rose Tuesday, helped by a rally in JA Solar (NasdaqGS: JASO) following upbeat quarterly results. [JA Solar Earnings Lift Green Energy ETFs]

Consumer staples ETFs followed the market higher Tuesday and received a lift from Dean Foods (NYSE: DF), which rallied over 10% after the dairy company raised its full-year outlook. [Dean Foods Boosts Staples ETFs]

Healthcare ETFs trailed the market as Boston Scientific (NYSE: BSX) slipped 8% after the maker of medical devices announced its chief executive will step down at the end of the year. [Healthcare ETFs Lag]

Gregory A. Clay contributed to this article.