18K just means "75% pure gold", it doesn't say what the other 25% is and there are a lot of different alloys. Most commonly it's mostly copper, which ironically is what gives it the standard "gold" tint (white gold uses metals like silver instead). I assume they mean "we picked an alloy that's harder than most".
Apparently Apple has their own metallurgists now... nauseating...
"crafted from 18-karat gold that our metallurgists have developed to be up to twice as hard as standard gold."
> Apparently Apple has their own metallurgists now... nauseating...
Given how many things they make out of metal, they've probably had metallurgists for years. I'm not sure what you find nauseating about that idea.
Did they really say that? Ha! Who knew my 9K gold stuff was vastly superior to higher grades.