Apple is making its iPhone 6 screen out of a substance known as sapphire glass according to popular rumors. The material, which is set to replace Corning’s Gorilla Glass in the device, is billed as the second-hardest material known to man—and almost impossible to scratch.

Sapphire glass has been used in watches for years, and that’s given us enough time to figure out how tough it really is. The answer is that the substance is incredibly tough, but it is nowhere near as shatter-proof as you might like. Feast your eyes on the gore of sapphire-faced devices throughout the article.

iPhone Pocket Sand

A video showing the resilience of the material emerged on the Internet yesterday to much aplomb. YouTuber Marques Brownlee somehow got his hands on the front panel of the iPhone 6. Through numerous tests the glass remained scratchless and unbroken. You shouldn’t expect that level of quality from your iPhone 6, however, and there’s a long history of tests to prove it.

The iPhone 5S and the previous iterations of the world’s most popular smartphone didn’t scratch all that easily. The Gorilla Glass used for the display managed to harden itself against most metals and other everyday scratching. On a hardness scale known as the Mohs scale, Gorilla Glass comes in at 6.8, while sapphire hits a 9. The only harder material on the scale is diamond, and that should mean that only a diamond can possibly scratch that beautiful iPhone 6 screen.

Gorilla Glass fell before the altar of pocket sand, that impossible-to-remove material. Sand contains minerals that are a good deal stronger than Corning’s glass, and so the screen of an older iPhone managed to scratch in everyday usage despite resilience to keys and other metal objects. Sapphire should hold up against that particular danger, but there are other, more threatening shadows lurking in the everyday usage of an iPhone 6.

Hardness Is Not Shatter Resistance

The biggest problem with iPhone screens over the years has not been scratching, it’s been shattering. There is no reason to believe that the iPhone 6 will be any different. As the pictures show, there is nothing invulnerable about sapphire glass. The iPhone 6 will not need to be dropped in a diamond mine in order to shatter. The tiles on your kitchen floor might be just enough to destroy the screen on the iPhone 6.

The shatter resistance of a material, while reliant on many other factors, is often linked closely with its scratch resistance. The more shatter resistant, the less hard the material is. Cheap plastic takes effort to shatter, but is scratched by the wind.

The iPhone 6 is going to be great, and Apple will sell the sapphire glass so hard it will defy reality. The YouTube video featuring the tests on the material is possibly a plant from the company, and many more should be expected before the year is out. Sapphire is not indestructible, however, so expect a bevy of complaints in Apple stores throughout 2015.

Disclosure: Author represents that he has no position in any stocks mentioned in this article at the time this article was submitted.