Apple may use super-strong sapphire screens on its iPhone 6 and iWatch, a new rumour suggests.

According to Canonical's CEO Mark Shuttleworth, Apple has just bought up enough sapphire screens to last about three years.

READ: iPhone 6 spotted with larger scratch-free sapphire crystal display, expected on the iWatch

This isn't the first time we've heard about Apple buying the screens - which are made of the second-strongest material on earth after diamonds. The initial news came from supply chain rumours, but whether it was meant for the iPhone 6 or iWatch wasn't clear.

According to Shuttleworth: "Apple just snapped up the entire three-year supply of the same sapphire display we wanted for the Edge." The Edge would have been a 4.5-inch device, had it reached its crowdfunding goal.

Of course this is based on Shuttleworth's comment so we must ask if the three-year supply is based on the usage of Canonical or Apple, which would clearly demand a lot more. Also the iPhone 6 will presumably be 5-inches so the 4.5-inch Edge screens wouldn't fit. But since it can be cut to size these may still appear on both the iPhone 6 and iWatch.

While we're at the rumour stage right now, sapphire displays - which won't be easy to scratch - appear to be coming soon.

READ: Apple iPhone 6 release date, rumours and everything you need to know