The word carat, the unit of measurement used when assessing the mass of gemstones and pearls, comes from the Italian word carato, which itself came from the Arabic word qīrāṭ (قيراط), which in turn came from the Greek word kerátion (κεράτιον)—the diminutive form of the Greek word kéras (κέρας), meaning "animal horn" (whence we get the word keratin, the protein that makes up your hair, skin, and nails). Thus, the word kerátion (κεράτιον) means "little horn." The word kerátion (κεράτιον) was also used to describe tiny carob seeds, which were occasionally used in antiquity as weights to weigh gemstones. As a unit of weight, a carat is 1/1728 of a pound. The term carat differs from karat (K), which is a measurement indicating the pureness of gold, specifically, the proportion of gold in an alloy out of 24 parts. Thus, 18K gold is 18/24 parts gold, which is nice, but an 18-carat diamond is very nice!