Apple has invested in the production of a new type of smartphone screen that is harder and more resistant to scratches, according to a report. Its new sapphire crystal production plant is expected to be up and running by the end of the month, but what has a precious gemstone got to do with smartphone and tablet computer screens?

What is it?

Sapphire is a super-hard form of optically transparent crystal that looks and behaves like glass or diamond.



Isn’t sapphire a precious stone?

Sapphire takes many forms, one of which is a gemstone. It comes in various colours including yellow, purple, orange, green and red. A red sapphire is known as a ruby, but the most recognised sapphire gemstone is of blue tint.



Won't sapphire crystal make my screen blue?

It’s the impurities in sapphire gemstones that give crystals their colours. The sapphire crystal used for screens, however, is colourless because it is more pure, lacking any of the iron, titanium, chromium, copper or magnesium that makes mined gemstones unique.



Is it dug out of the ground?

Sapphire gemstones are commonly mined like most other precious gems, but the sapphire crystal used in most non-jewellery applications is artificially manufactured.



The first synthetic sapphire was created in 1902 by a French chemist called Auguste Verneuil. Since 1902 various methods of making sapphire have been developed, but generally they use high heat and pressure to turn aluminium oxide power into crystal.

A video showing how artificial sapphire crystal screens are created.

Where is sapphire crystal currently used?

Most synthetic sapphire is used in industrial processes, but some colours of sapphire are useful for laser applications. Red ruby sapphires are used to create red and new-infrared lasers thanks to their relatively unique capacity to be turned to the appropriate wavelengths, thanks to their titanium or chromium impurities.



Sapphire crystal is also used in protective windows, including bullet proof glass and the viewing windows for high pressure diagnostic and scientific equipment. The glass-like material covering supermarket barcode scanners is often sapphire crystal due to its scratch resistance.



The most common consumer application for sapphire crystal is in the creation of extremely hard and scratch-resistant coverings for lenses or high-end watch faces. Rolex watches, for instance, have thick sapphire crystal watch faces, while the home button and TouchID sensor of Apple’s iPhone 5S is covered by a laser-cut sapphire crystal lens.



Where is sapphire crystal likely to be used in the future?

Some very high-end smartphones currently use sapphire crystal screens. The handmade Vertu Ti, for instance, has a 3.7in crystal-covered screen, but sapphire crystal has historically been too expensive for mass produced smartphone screens.



A recent report stated that Apple is actively looking at replacing its glass iPhone screens with sapphire crystal. According to data from the supply chain, Apple has acquired the machinery and facilities necessary to make display-sized crystal in enough volume to build into future iPhones.



Why would you want it over normal glass?

Compared to regular glass, sapphire crystal is significantly harder and therefore much more scratch resistant, an important factor for screens and other optically clear coverings like camera lenses.



The hardness of a material is rated in Mohs, where talc is rated as 1 Mohs and diamond 10 Mohs. Glass ranks around 5.5 to 7 Mohs, but sapphire crystal has a hardness of 9 Mohs, making it only slightly less hard than diamond.



The Mohs rating of Corning’s Gorilla Glass, which is the chemically hardened glass used to make many smartphone screens including those found on the Google Nexus 5 and Samsung Galaxy S4, has not been released, but it is expected to be around 7 Mohs.



Regular steel has a hardness of around 4 Mohs, but hardened steel a hardness of around 8 Mohs. Anything made of a substance that is harder with a higher Mohs rating will scratch anything that is not as hard, meaning a sapphire screen could resist scratches from almost anything likely to be carried in a pocket.



How much will sapphire crystal screens cost?

One of the reasons that sapphire crystal has not been used for smartphone screens has been its relatively high cost. Corning claims that Sapphire crystal screens would cost around 10 times as much as its Gorilla Glass.



If Apple is serious about making iPhones with sapphire crystal screens it is unlikely to cost the consumer any more. The new iPhones with sapphire screens would likely be priced similarly to the current iPhone 5S.



Are there any competitors to sapphire crystal in screens?

There are a couple of different manufacturers and glass-like products competing for the smartphone and tablet screen. The most well know is Corning and its Gorilla Glass, which is in its third iteration and is found on many smartphone screens including the Samsung Galaxy S4. The alkali-aluminosilicate glass combines impact resistance with increased scratch resistance, but is also strong allowing the screen to be very thin.



Japan’s Asahi Glass Co has its own competitor called Dragontail, which has similar properties to Gorilla Glass and is found on the Sony Xperia Z1 as well as the Samsung Galaxy Nexus smartphones.



Sapphire crystal is harder than both these two glass products, and therefore more resistant to scratching, but could be less resistant to impact and fracturing. In its currently available form, sapphire crystal cannot be created as thinly as glass and therefore leads to heavier screens. It is unknown whether Apple has developed a way to make thinner, stronger sapphire crystal screens.



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