What is 24K gold?
24 karat gold is essentially pure gold — 999 fineness, meaning at least 99.9% gold content with only trace impurities. On the karat scale, purity is measured out of 24 parts, so 24K means all 24 parts are gold. Because no harder alloy metals are mixed in, 24K gold is soft and easily scratched, which is why it is used mainly for bullion bars, investment coins, and gold savings products rather than everyday jewellery.
Some refiners produce 999.9 ("four nines") gold, which is even purer. For pricing purposes 999 and 999.9 gold trade at effectively the same rate: the international spot price of pure gold.