Apple may be planning on using its sapphire glass on just the rumored iWatch, and not on the iPhone 6. Assuming the sources sharing the information are correct, it looks like the decision to limit the sapphire glass to the still mythical smartwatch is based on cost: It's just too expensive to use on the iPhone.
News of Apple's plans comes courtesy of unnamed Taiwan supply chain sources speaking with My Drivers (English translation) and PC Pop (English translation). The sources claim Apple has been testing iPhone prototypes with sapphire glass touch screens, but they aren't expected to become production models because the material is currently proving to be too expensive in the sizes the company needs.
Sapphire glass has properties that make it ideal for some portable electronic devices. It's surprisingly hard and strong, and very clear, so it's less likely to break under normal abuse and won't distort the display surface it protects.
The material does make sense for the iWatch display since its durability would make the display more resistant to the type of abuse it would likely encounter in day to day use. Apple has been hiring fitness and health related experts for the past couple years, hinting that its wearable tech plans may include activity tracking -- an area where a stronger device face would be especially useful.
The screen size on the iWatch is expected to be about 2-inches, and at that size the sapphire glass wouldn't drive up the device's price like it would on the iPhone.
That said, Apple seems to be preparing to manufacture large amounts of the highly durable material. A recent report showed Apple has been working with GT Advanced, the company that's manufacturing its sapphire glass in Arizona, to produce enough material for 200 million iPhone displays.
If all that sapphire glass isn't destined for the iPhone, that means Apple is planning on making massive numbers of its rumored smartwatch. That's possible, but it also seems likely that Apple plans to start using sapphire glass on the iWatch, and then ramp up production to handle its iPhone needs later -- assuming it can keep the price down.
Of course, Apple is keeping quiet about its future device plans and isn't talking about what it has in store for wearable technology. What we know for sure is that Apple is very interested in the wearable tech market, has plans to move into new product categories in the near future, and has a factory capable of producing massive amounts of synthetic sapphire glass. That sounds like a pretty exciting mix.
[Thanks to G4Games for the heads up]