Apple has got a thing for sapphire.

According to the latest insider knowledge close to Apple, GTAT's Salem, Massachusetts sapphire facility has been ramping up sapphire production for Apple's benefit since late 2013.

In short, it now appears that Arizona is not the only market where Apple is growing its appetite for the crystalline material.

The latest regulatory filing from GT Advanced Technologies (GTAT) confirms that the company has teamed with Apple (which issued a $578 million prepayment) to jointly expand and operate the plant in question.

Matt Margolis of Seeking Alpha explains that the new details made public for the first time this week include: "intended target dates for GT to occupy and grow sapphire, additional clarity around some of the prepayment dates, additional information related to Apple's prepayment, which includes retrofitting and qualification of sapphire growing at GT's Salem, MA facility as well as the capital build-out of the Mesa, AZ sapphire facility and lastly GT's requirement to raise additional funds via debt or equity financing."

Source: Seeking Alpha