@freemo It appears this 4nm layer is amorphous (or at least polycrystalline), not corundum/sapphire, unless produced by plasma oxidation with the express purpose of producing hardened aluminum oxide for increased hardness. Additionally, while clear, pure, alpha-crystalline aluminum oxide is often called sapphire (for what I think must be a marketing gimmick) it is actually just pure corundum, as sapphire is corundum with the metal ion inclusions that aren't red (which is ruby).
But the aluminum passivity layer is pretty sick from a materials/chemical perspective for sure :3
@johnabs While blue sapphire and other colored sapphire does indeed have things in it other than aluminum oxide giving it its color dont forget clear sapphires. Those are just crystalline aluminum oxide.
Did not know that the layer on aluminum was amorphous though, fair point.
@johnabs Clear corundum occurs naturally and is often called clear saphire. So I wouldnt really call that a gimmick. Ruby, yes, they must be red, they are just red sapphires as you know. But no sapphire was never restricted to just blue as far as I know.the other color of sapphires are still called sapphires, at least since the 80s when i started collecting them.
@johnabs Oh well yes if your talking ancient times then sapphire originally referred to only the blue ones. In fact they had no idea clear sapphires were sapphires at all.
Sapphire and Ruby are terms generally used more in marketing, though i still wouldn't call a gimmick, its just how the word evolved. Geologists almost always call it corundum in my expiernce, particularly when talking in the general sense (inclusive of all colors).
@johnabs Also dont get started on the absurdity of human naming things... I've been ready to use a constructed language for decades :)
@freemo I could be wrong on the reasoning, but I believe the term sapphire exclusively referred to the blue variant (and possibly lapis lazuli) from an etymology perspective. It is a VERY old word, in fact.
Maybe it's not a marketing gimmick just natural language evolution, but in that case, why call them sapphire or ruby at all? Just call em *Corundum(or *Sapphire), where * is the RGBAOCCCC (rgba+optical orientation+the 4Cs) of the gem. Maybe it doesn't roll off the tongue? XD
WHO DEVISED THIS TERRIBLE NAMING SCHEME? I NEED ANSWERS FREEMO, WHY ARE PEOPLE LIKE THIS?!