Penglai deposit near Wenchang on Hainan Island.
Sapphire-bearing alluvial deposits occur at depths of 1.5 to 3 m from the surface and contain fragments of olivine basalt and pyroclasts, as well as pyrope
and other minerals. The sapphires
are most often dark blue, greenish-blue and green, and less often pale blue and yellowish-green. The crystals have a hexagonal-prismatic habit, average size 2 - 5 mm. Larger grains maybe 3 - 3.5 or more in size. The refractive index is 1.761 - 1.769, the density is 3.99 - 4.02 g/cm³.
Ref: E.Ya. Kievlenko (2003) Geology of gems, p. 68