The rubies found here are dark red in color with brownish tinge. Sometimes they resemble garnet. Some of the pieces are stunning almost as good as Burmese rubies but majority of the stones are dark in shade with inferior quality. The mines of Chantabun are located in the vicinity of the Gulf of Siam, and near the town of Chantabun. The area has grayish granite mountains with the limestone lowlands. It is held that the latter may be the mother-rock of the ruby.

At present the precious stone are found in the sands, which are mined by the locals using traditional methods. The other ruby mines are scattered over the area in Krat located near Chantabun. These mines are divided into two groups Bo Nawang and Bo Channa.In the mines of Bo Nawang they are usually found in small pits which are 2 to 4 feet deep. The rubies are in the base of the six to ten inches thick sand .Bo Channa mines are located thirty miles northeast of Bo Nawang and spread over a mile square area .The rubies are found in six to twenty four inches thick sand .Some of the mines are as deep as 24 feet. The ruby district of the sub-province of Muang Klung is located between the provinces of Chantabun and Krat.The gem mines are found in the valley and on the sides of the hills. These valleys are crisscrossed by small streams. It is on their banks the gems are found in alluvium deposits in the dry season. During rainy season miners concentrate on deposits on the sides of the hills. The gem-bearing clayey layer has 10 inches to 5 feet thickness where rubies are found more frequently than other gemstones like sapphires. Few rubies are also found in the sapphire mines of Battambang located southeast of Bangkok.

This material's main attribute is its high clarity, but the flat crystal shapes generally yield overly shallow stones. Due to the high iron content, which quenches fluorescence, most stones tend to have a garnet-red color. An additional problem is the total lack of light-scattering silk inclusions (star stones are not found). Although heat treatment does make improvements, it is not enough. In Thai/Cambodian rubies, only those facets where light is totally internally reflected will be a rich red; the others appear blackish, as with red garnets. Thai stones are actually less purple than most Burmese rubies. However, Burma-type rubies appear red all over the stone. Not only is a rich red seen in the areas where total internal reflection occurs, but due to the red fluorescence and light-scattering silk, other facets are also red.

With the decline in Burma production during the 1962–1990 period, the market became conditioned to Thai/Cambodian rubies, with some people actually tending to prefer them (in the land of the blind, the one-eyed man is king).

Thai/Cambodian rubies are acceptable only when good material from the Burma-type sources is not available. Today, production from the Thai side of the border is zero, and that from Cambodia is negligible. One occasionally hears statements about how Cambodian stones are superior to those from across the border in Thailand. This is untrue. The deposits are essentially one, directly straddling the border.

Ruby, natural, Thailand

In Thai rubies, one of the characteristic inclusions consists of a core with rings around it ("Saturn" inclusion) or a fingerprint pattern that either cuts through the core's centre or rests against it. If there are several Saturn inclusions, they all tend to be orientated parallel to each other.

  • very few or no rutile silk needles
  • no exsolved particles(unlike Burmese rubies)
  • polysynthetic twinning common, often incorporated with long, thin, whitish boehmite needles
  • rounded feldspar and apatite guest crystals
  • saturn inclusions with dotted texture are common
  • colour zoning very rare
  • liquid inclusions common, forming fingerprints or healed fractures
  • hexagonal crrystal growth lines
  • weak to moderate red or red/orange in LW, inert or moderate reddish/orange in SW(natural)
  • rutile silk needles are rarely encountered
  • very uneven colour zoning accompanied by exsolved coarse particles of unknown nature, concentrated and following the blue colour zoning(not the colourless areas) producing a characteristic slightly milky overall appearance
  • solid guest crystals: feldspar, hornblende, pyrrhotite, etc
  • Polysynthetic twinning
Thailand - once about 70% of world production. Important because of lack of commercial mining in Burma.
  • Darker red; brownish to purplish overtone due to Fe
  • 85-90% from the Chanthaburi-Trat gem field (since 1850?), 330 km SE of Bangkok.
  • Mining restricted to Thai nationals since 1919.
  • In lateritic soils atop Plio-Pliestocene basalt, or in gem gravels derived from basalt. Deposits are about 6-20' below the surface.
  • Source is thought to be basalt (corundum xenocrystic?).
  • More Fe-rich than Burma ruby, show a much weaker red than Burmese stones in short and long u.v..
  • Characteristic inclusion is pyrrhotite (iron sulfide).