As we climb higher and higher up the mountain along a worn path through the dense forest, I wonder if it’s possible for us to melt in the 40°C Cambodian heat. It’s an arduous hike, but our surroundings and the minerals we’ve come to see make the trip worth it.

Museum scientists hiking down a dusty trail on Phnom Bayong in Takeo province, Cambodia.
Hiking down Phnom Bayong. Image: Paula Piilonen © Canadian Museum of Nature

We’ve come to the south of Cambodia, along the Vietnamese border, to study Phnom (mount) Bayong, a granodiorite mountain that hosts pegmatites containing beryl (var. aquamarine), topaz, smoky quartz and fluorite. After two hours of slogging our way up through the forest, we arrive at the miner’s current workings. High above the town of Kirivong, the miners are using traditional methods to break apart the granodiorite that makes up Phnom Bayong, to extract fluorite from veins to sell to gem dealers, tourists and locals.

Fluorite—CaF2—is sought after by mineral collectors, lapidary artists and the larger mineral industry. It occurs in a wide variety of colours and forms, the most common of which are green or purple cubes; however, blue, pink, yellow and colourless fluorite in octahedra and rare dodecahedra can also occur. This diversity of colour, form and habit gives fluorite great aesthetics and makes it a popular mineral among collectors.

Commercially known as “fluorspar,” fluorite has been used as a flux in the smelting of iron ore since the 1500s, and more recently in the production of aluminum and steel. It is also used to produce hydrogen fluoride and in the manufacture of glasses and enamels.

Fluorite was first mined in Canada from deposits at St. Lawrence on the southeast coast of the Burin Peninsula in Newfoundland. Discovered in 1843 and commencing production in 1928, the St. Lawrence deposits were the largest known in North America at the time. Veins and lenses of fluorite kilometers long and up to 10 metres thick were mined by hand under back-breaking conditions, at first in surface trenches and later underground. Operations expanded extensively after World War II as the demand for aluminum and steel rose. By the 1970s, increased competition from other countries drove down the price of fluorspar ore. As a result, operations at St. Lawrence, then owned by ALCAN, were ultimately shut down. In 2018, Canada Fluorspar Inc. (CFI) put forth a proposal to resume mining operations.

A miner works underground in harsh conditions at the St. Lawrence Fluorspar mine during the 1970s.
St. Lawrence miner, circa 1970. Image: © Heritage Newfoundland & Labrador.
A photograph of the head frame and mill at the Director Mine, St. Lawrence Fluorspar mine, taken around 1960.
Head frame and mill at the Director Mine, St. Lawrence Fluorspar Mine, circa 1960. Image: © Heritage Newfoundland & Labrador.

No powered equipment is used to mine the fluorite at Phnom Bayong—hauling generators up the mountainside is not practical. The workers revert to a centuries-old technique of fire-setting to crack the rock. Fire-setting was one of the most popular mining methods until the invention of dynamite by Alfred Nobel in 1866; however, dynamite is hard to come by in Cambodia.

A miner works in a trench to extract fluorite from a vein.
Miner in a trench. Phnom Bayong, Takeo, Cambodia. Image: Paula Piilonen © Canadian Museum of Nature
A vein of purple and green fluorite within the granodiorite at Phnom Bayong.
Fluorite vein. Phnom Bayong. Image: Paula Piilonen © Canadian Museum of Nature

The workers cut down trees and lay them in the trench. A fire is set and left until it burns itself out. The heat from the fire expands the rock, after which it is quenched with water to create cracks. The broken rock can then be chiseled and hammered at to expose a fresh layer. Another fire is set, and the process continues until the fluorite is reached. It is hard work, but the fluorite pieces can be sold in the gem market at the base of the mountain for more money than an average Cambodian makes in a single day.

Logs in a trench are set on fire to expand the rock.
Fire cracking of the granodiorite. Phnom Bayong. Image: Paula Piilonen © Canadian Museum of Nature
Mr. Sokphun holds up a large piece of green and purple fluorite from his mine.
Mr. Sokphun, fluorite mine owner. Image: Paula Piilonen © Canadian Museum of Nature

The gem mines at Phnom Bayong are not well-known, except to the locals and a few gem dealers. Our research in the region, however, will help shed light on the mineralogy and genesis of the deposits, and help increase the overall geological knowledge of the country.

Mineralogist Paula Piilonen meeting some of the local dogs while examining mineral samples.
Meeting some of the locals at the fluorite mine. Phnom Bayong. Image: © Sovanny Ly
Paula is holding a small, light-green cube of fluorite that was found in a pegmatite within the granodiorite at Phnom Bayong.
A small (3 cm) green fluorite cube from a pegmatite in the granodiorite at Phnom Bayong. Image: Paula Piilonen © Canadian Museum of Nature