Trat Province is situated in the northeastern coastal belt of the Siam Gulf. It borders with Chanthaburi Province
. The combined area is sometimes referred to as the Chanthaburi-Trat gem region.
This rich gem region, which produces about 90% of the Thai rubies and sapphires, as well as some zircons, is in southeastern Thailand on the western slopes of the Dangrek Range, near the boundary with Cambodia.
The deposits are dominantly alluvial placers derived from the weathered underlying basalts. Eluvial residual placer deposits have been reported.
Rounded grains, less than 5 mm and rarely as large as 1 cm or more, are representative of the rubies
from Trat. Their intense violet tint is characteristic, although some are the highest quality red rubies
of "pigeon's blood" colour. Refractive index is 1.766 - 1.774, density is 3.97 - 4.05 g/cm³.
Solid inclusions of pyrrhotite, apatite and very rare garnet.
Ref: E.Ya. Kievlenko (2003) Geology of gems, pp. 44, 66
Gem list contains entries from all listed localities in region.
Localities in this Region