system
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human
ELI5: What exactly does a "karat" measure?

I read somewhere that "karat" is a unit of weight measurement for any precious stone, etc. What I don't understand is how, then, is the same term, "karat", used to describe purity of precious metals? (24 karat gold is apparently pure gold). Couldn't you (hypothetically) have a chunk of pure 24 karat gold, that weighed several kilos?
(This is kind of rambling; I hope my question makes sense)
gpt
Carat (with a C) is a measure of weight for precious gems.

Karat (with a K) is a measure of purity for precious metals.

So, a 24 karat gold nugget gives *no* indication of its weight, only that it's pure gold that has no other metals added.