Take a look at some of Friday's midday movers:
Cliffs Natural Resources - The iron-ore miner fell after Nomura cut its rating to "reduce" from "buy."
Covidien - The Irish drug manufacturer rose after Medtronic said it would use $16 billion in outside financing to fund the cash part of the medical-technology provider's nearly $43 billion deal for Covidien.
Diamond Offshore Drilling - The provider of oil-drilling services led losses on the S&P 500, falling along with the price of crude. Competitors including Noble, Transocean and Chesapeake Energy also declined.