NEW YORK (TheStreet) -- GT Advanced Technologies (GTAT) was gaining 5.1% to $18.84 Tuesday after Piper Jaffray initiated coverage of the company with an "overweight" rating.

The analyst firm set a price target of $23 for the company. GT Advanced shares will "likely react sharply" to Apple's (AAPL) - Get Report iPhone 6 which may use the company's sapphire crystal glass, according to analyst Mike Ritzenthaler. "We believe that Mesa process yields (though perhaps currently suboptimal) are sufficient to cover the initial production of the iPhone 6, and poised to improve over the next 6-9 months," Ritzenthaler wrote.

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GTAT data by YCharts

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