What is sapphire glass and why is it in the next iPhone?

It seems all but certain Apple will be making the switch to sapphire glass for the iPhone 6 screen, a radical departure from the hardened Gorilla Glass it has been getting from Corning since the first iPhone came out in 2007. Until now, sapphire glass was only used on the camera lens of Apple’s devices, but the technology now exists to make it a viable options for the entire front panel. It’s probably not going to be cheap, but sapphire glass could become the next must-have feature in smartphones.

When you hear the word “sapphire,” you’re probably thinking about a shiny blue stone that costs a bundle of money, but that’s not quite what sapphire glass is. In other words, it’s going to be expensive but not that expensive. A stone can technically be a sapphire and have none of the characteristic blue coloring. As with most precious gems, the color is the result of impurities, in this case mostly chromium and titanium. The sapphire used for glass has none of that.

Of course, no one is digging stones out of the ground to make into phone screens. The glass on the upcoming iPhone 6 will be produced in a lab.

Sapphire is the third hardest mineral in existence — it scores a 9 on the Mohs hardness scale right behind diamond at 10 and moissanite at 9.25. Sapphire is still very durable compared to most materials you might use on a touch screen. Sapphire glass isn’t just hard to crack, it’s also very difficult to scratch. That’s probably a more common issue with phones than a completely shattered screen.

Does that mean it’s all good news for sapphire glass phones? Well, there is the issue of mass. Sapphire glass has a density of 3.98 g/cm3, which is 67% higher than Gorilla Glass at 2.54 g/cm3. So for the same thickness of glass, the sapphire panel would weigh quite a bit more. Screens actually account for more of the weight than you’d think — a sapphire screen could add over 100g to the mass of a larger iPhone. So users might be surprised by the heft when they pick up the iPhone 6. Cost might also be a concern, but Apple wouldn’t be going ahead if it didn’t have the supply chain sorted out.

Everyone (or almost everyone) seems happy with the resolution of screens these days, so maybe sapphire glass is the next step. After all, that screen won’t look pretty when it’s covered in a spiderweb of cracks. [via Geek]