Corundum deposits in the border region between Cambodia and Thailand have been well-known for hundreds of years among local populations but were popularized to the West during the late nineteenth century when H. Warrington Smyth published his book, Five Years in Siam, in 1898. Most of the gem deposits in current-day Cambodia occur in the Western province of Battambang, particularly near the town of Pailin.
The first stones ever to be treated with heat to improve their colors allegedly originated from the Pailin mines in Cambodia. Cambodia is famous for commercializing gem treatment, which was later passed on to the Thais. According to gemologist Richard Hughes, there are two different accounts of how heat treatment became commonplace along the Thai-Cambodian border. The process was apparently invented by Professor and Madame Bron of Company Grasset and Bron in Geneva. During the French colonial era in Cambodia, it was common for the elite to visit distinguished intellectuals and two Cambodian visitors to the Brons passed on their treatment method to local dealers.
The sapphires of the Pailin area are considered fairly valuable and during the time of the Khmer Rouge in the seventies and eighties, these gems were allegedly used for arms purchases. Given the intensity of the conflict in this region of Cambodia, the land is heavily mined and mineral operations are now extremely dangerous. There is extensive use of hydraulic mining in this area which has led to widespread erosion. Individual diggers are also observed in many parts of this area given the extreme level of poverty that is pervasive in the region.
While Oxfam has done considerable work on the environmental impact of gold mining in Eastern Cambodia, very little research or activism has occurred on the environmental impact of gemstone mining in the Western part of the country. However, Hollywood star Angelina Jolie has invested more than $5 million (over the next 10 years) in environmental projects near Pailin through her foundation (in honor of her Cambodian adopted son Maddox). The work of the Maddox-Jolie-Pitt Project is partly administered by San Francisco-based Wild Aid and aims to protect more than 20,000 hectares (49,500 acres) of forest in northwest Cambodia, which five years ago was still controlled by remnants of the Khmer Rouge.
Due to this attention, there are plans by the provincial government to start tourism projects in the area once the land has been de-mined. One of the projects that our team visited during research in this area was a restored mine that has been converted into an aquaculture pond and a recreational lake (see photo below).
The map below is from Chapter 12 of Ruby & Sapphire by Richard W. Hughes.
The map below is from an article by Richard W. Hughes, who is a gemologist and expert on rubies and sapphires.
 Abuza, Zachary. “The Khmer Rouge’s Quest for Economic Independence.” Asia Survey, Vol. 30, No. 10, 1993.
 Knight, Katherine 2003. Cambodia: War Politics and the Environment. Conservation Law Foundation.
 Richardson, Michael. “Breakaway Faction Controls Gem Mines That Sustained Group: Defections Shake the Khmer Rouge,” International Herald Tribune, August 12, 1996.