Apple is reportedly ready to use the ultra-tough sapphire crystal for the displays of the forthcoming iPhone 6.

According to the Wall Street Journal, Apple and GT Advanced Technologies Inc. are set to start mass-producing displays for a 4.7- and 5.5-inch iPhone. Apple's next handset is expected to be unveiled in early Sept. with a release weeks later.

Apple and GT had previously opened a sapphire crystal plant in Mesa, Ariz. and the tech giant was immediately believed to be widening its use of the scratchproof material. Apple already coated its Touch ID fingerprint sensor and camera lens in sapphire crystal.

"Nobody has ever invested this much money on sapphire," Eric Virey, a senior analyst at French research firm Yole Développement, told the Journal of Apple's $700 million venture.

Neither Apple nor GT commented on the matter, but Virey said the switch would be an expensive one. Currently, Apple spends about $3 per Gorilla Glass display, but sapphire crystal would come at about $16 apiece.

The change is also expected to force Apple to hike up the prices, though spending extra might be a good investment, as the displays will be near completely immune to drops. It is not clear if cellular providers will raise the price of the device with a two-year contract, but it is certainly a possibility.

Ming-Chi Kuo, an analyst at KGI Securities and a trusted source for Apple rumors, previously told Mac Rumors the 5.5-inch iPhone 6 would be released weeks - possibly months - after the smaller version. Kuo said he expected the 4.7-inch model to be released in mid-Sept., as is customary for Apple.

Re/Code learned that Apple's unveiling event for the iPhone 6 will be Sept. 9, making a Sept. 19 release highly plausible. If Kuo is right about the two different release dates, Apple could potentially hold off on releasing their larger iPhone 6 to give GT more time to produce the necessary volume of sapphire displays.