Earlier quoted context omitted.
> Moissanites have already become as near-worthless as synthetic rubies. I've noticed that synthetic sapphires are (or were?) much more expensive than synthetic rubies. Do you know why?
I'm also curious about this. Especially since natural rubies and natural sapphires are the same type of gemstone, just in different colors. It sounds like the synthetic equivalents might not be similar at all!
A ruby is corundum with chromium coloring it; a sapphire is corundum with (most typically) iron coloring it.
Iron isn't rare, so either it affects the process used to make rubies, or there's no real reason for the price gap.