pearl grain

A unit of mass used in the pearl trade, such that 600 pearl grains = 1 troy ounce, so 1 pearl grain = ⁴/₅ of a grain, about 51.839 milligrams.

In Australia and New Zealand, the grain, as applied to pearls, was ¼ of a carat of 205.5 milligrams, or 51.4 milligrams. This unit, perhaps coincidentally, bears the same relationship to the carat (¼) as the old Islamic pearl grain, the ḥabba, bore to the ḳirāṭ.