Sapphire crystals are made from aluminium oxide powder, compared to silicon dioxide in standard glass.
Sapphire crystals are made from aluminium oxide powder, rather as standard glass is made from silicon dioxide.
It is formed of alternating layers of aluminium oxide and sodium ions.
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.
The filling of the sandwich was an insulating layer (usually aluminium oxide) that was only a few molecules thick.
About five tonnes of that are chemically refined, usually near the mine, into two of alumina, an aluminium oxide.
It consists of a relatively small lump of aluminium oxide into which a hole has been bored.
It uses a heat-resistant layer of aluminium oxide to insulate the battery's electrodes, instead of the usual layer of polyolefin plastic.
"I would smash the thing up, stick it under a microscope and you'd have your answer as to whether this is aluminium oxide (sapphire) or silicon dioxide (glass)," said Alford.
It has been possible to manufacture the gem for more than a century, using a process involving dipping a small "seed" into a vat of molten aluminium oxide, of which sapphire is a crystal.
