Abstract— A new empirical cooling rate indicator for metal particles is proposed. The cooling rate indicator is based on the relationship between the size of the island phase in the cloudy zone, which abuts the outer taenite rim (clear taenite I), and the cooling rate of the host meteorite as obtained by conventional metallographic techniques. The size of the island phase was measured by high-resolution scanning electron microscopy (SEM) in 26 meteorites and decreases from 470 nm to 17 nm, while the cooling rate of the host meteorite increases from 0.5 K/Ma to 325 K/Ma. This island phase size vs. cooling rate relationship is independent of whether the host is an iron, stony-iron, or stony meteorite and can be used to estimate the low-temperature cooling rate of the host meteorite. The measurement of the size of the island phase in the cloudy zone can also be applied to a large number of meteorites.