gemmology.dev – Cambodia – Pailin Sapphire and Battambang Ruby

Introduction

Cambodia produces two geologically distinct corundum types. The Pailin Province field in northwestern Cambodia sits within the same Cenozoic alkali-basalt province as Thailand's Chanthaburi-Trat deposits, separated only by the Thai-Cambodian border, and yields high-iron basaltic sapphires and ruby with the hallmark Fe-rich geochemical signature: >600 ppm Fe, strong 450–470 nm triplet absorption, and weak LWUV fluorescence due to iron quenching chromium. A second, geologically distinct occurrence of marble-hosted ruby exists near Battambang, analogous in principle to Mogok and Luc Yen, with low Fe and stronger fluorescence.

Pailin gem production was severely disrupted during the Khmer Rouge era (1975–1979) and subsequent civil conflict, halting international trade access for two decades; material from that period was documented as a Khmer Rouge revenue source. Modern laboratory separation of Pailin from the adjacent Thai Bo Rai deposits requires LA-ICP-MS trace-element analysis of Ga/Mg, Fe/Ti, and Cr/Ga ratios alongside oxygen isotope data. ^[1]^[2]

Geological Settings

Two corundum-forming environments in Cambodia:

Pailin — Basaltic Province

Cenozoic intraplate alkali basalt field; same Southeast Asian province as Chanthaburi-Trat (Thailand) and Ratanakiri (also Cambodia, for zircon)
Corundum transported to surface in basalt; concentrated in alluvial placers
High-Fe, low-Cr geochemical environment; same signature as Thai basaltic material
Adjacent to Bo Rai (Thailand); material from both sides historically mixed

Battambang — Marble-Hosted Ruby

Small-scale occurrence of marble-hosted ruby, geologically analogous to Mogok and Vietnam marble-type deposits ^[3]
Low-Fe environment; strong fluorescence expected
Much smaller production volume than Pailin
Geologically distinct from the Pailin basaltic deposits

Khmer Rouge Era Hiatus

Pailin Sapphire and Ruby — Diagnostic Features

Characteristics of Pailin basaltic corundum:

Colour

Sapphire: Blue to green, yellow, and parti-colour; broad range typical of basaltic sapphires
Ruby: Dark red; comparable to Thai basaltic material but with subtle differences in trace element ratios

Chemistry and Spectroscopy

High Fe: Basaltic geochemical profile; >600 ppm Fe typical ^[1]^[2]
Strong 450/460/470 nm triplet: Fe-related absorption in UV-Vis spectra, similar to Thai material
LWUV fluorescence: Weak; iron quenches chromium signal
Oxygen isotopes: Values consistent with basalt-related corundum

Inclusions

Basalt-suite minerals: zircon (with halos), feldspar, iron oxides (ilmenite)
Consistent with basaltic parentage; same mineral family as Thai material
No marble-hosted inclusions (no calcite, apatite, sphene)

Pailin vs Thai Distinction

Separating Cambodian Pailin from Chanthaburi-Trat:

Historical difficulty: Pailin and Bo Rai (Thailand) material was historically traded together through Chanthaburi and often mixed; laboratory separation was not routine ^[4]
Modern LA-ICP-MS: Trace element ratio patterns (Ga/Mg, Fe/Ti, Cr/Ga) and oxygen isotope analysis can discriminate Pailin from Chanthaburi with some confidence; the separation is a laboratory-level task
Practical trade note: Material described as "Thai ruby" in the trade may include Cambodian origin stone heated in Thailand

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Cambodia – Pailin Sapphire and Battambang Ruby