iPhone 12 and its glass-ceramic shield

Corning’s new iPhone shied is made of a novel nano glass-ceramic. It consists of nanocrystals embedded within the glassy matrix. The crystals are smaller than the wavelength of light and refractive index-matched to the glass. That’s why the material is highly transparent, unlike other glass-ceramics. Furthermore, the crystals form interlocked structures that result in high flaw resistance and provide a mechanism to deflect and arrest cracks. The glass matrix is strengthened by ion exchange to provide a high degree of retained strength after damage.