The sapphire deposit at Penglai, on Hainan Island, is potentially the largest in China. Gem-quality sapphires, at least one as large as 35.5 ct, have been found in alluvial gravels approximately 2 km southeast of the city of Penglai. Gem-quality zircon and a few pieces of what might be considered ruby have also been recovered in the course of the geologic study of this area, which has not yet been commercially developed. The average size of the sapphires is 2—5 mm. They are similar in appearance and gemological properties to sapphires from Australia, Thailand, and Kampuchea.