A video posted on YouTube on Friday shows an alleged iPhone 6 front glass cover being tortured by garnet sandpaper. The glass comes away scratched, suggesting the part is not made of sapphire.
… the part supposedly bound for Apple’s iPhone 6 shows surface scratches after being rubbed by garnet sandpaper, suggesting the glass is not made of sapphire. In the video, YouTuber Marques Brownlee also shows the cover glass failing to resist scratches from emery sandpaper, which is much harder than garnet.
Brownlee explains the Mohs scale of relative hardness in the video, saying a material with a higher rating cannot be scratched by one assigned a lower number. Sapphire rates 9 out of 10 on the Mohs scale — while garnet is a 7. Emery is a mixture of corundum and magnetite and is assigned an 8 on the Mohs scale. Neither should be able to scratch Sapphire.
The only mineral harder than sapphire is diamond, with a relative hardness of 10 on the Mohs scale.
To further prove his point, Brownlee takes the same sandpaper to the iPhone 5s, which has a screen made from Corning’s Gorilla Glass. The display area is shown to be scratched, while the sapphire-covered Touch ID home button comes away without a scratch.