Further adventures of our mineralogists in Cambodia: follow museum scientists Paula Piilonen and Glenn Poirier on their hunt for minerals for their research.

In Ratanakiri province, and many other regions across Cambodia, the land is covered by a dark orange red, iron- and aluminum-rich soil called laterite.

Images: A red dirt country road; a look down at a red-dirt encrusted boot.
Laterite dust covers all the roads in the region! Laterite dust turns all your clothes red. Some days it’s hard to tell if I am tanned or simply dirty! ☺ Images: Paula Piilonen © Canadian Museum of Nature

Laterites form in tropical climates and are the result of extensive, intense chemical weathering of the underlying rock—in this case, basalt.

Basalt forming a round shape in the ground beside a geologist's hammer.
In situ weathering (spallation) of basalt to form laterite. Image: Paula Piilonen © Canadian Museum of Nature

When wet, laterite can be cut into blocks and used for construction of buildings. As it dries, it hardens to a rock-like consistency. The Angkor Wat complex, along with many other temples of Angkorian age (9th and 10th centuries) found throughout both Cambodia and Thailand, have been constructed with laterite bricks as the main foundation, covered with more aesthetic sandstone facing.

Carved stone structures at an ancient temple.
Laterite bricks form the internal foundation of Banteay Srei temple, 23 km north of Angkor Wat (10th century). Image: Paula Piilonen © Canadian Museum of Nature

Because laterite profiles in this part of the country can be up to 50 metres thick, it is sometimes difficult to find fresh, solid rock outcrop. For this reason, our field work tends to focus on areas that provide the most likely exposure: waterfalls, rivers/creeks, boulder fields at the bottom of slopes, and quarries.

A woman stands near a small waterfall.
Paula Piilonen at the Katieng Waterfall, Ratanakiri province, Cambodia. The waterfall goes over a basalt flow. Image: Glenn Poirier © Canadian Museum of Nature

Today we visited one such quarry north of Ban Lung and the Angkor Gold office. Here, they are quarrying basalt, the rock that we are studying, for use as road fill. After poking around the waste-rock piles on the edges of the quarry near the stone crushers, we met one of the workers who, through hand gestures because he didn’t speak English and we don’t speak Khmer, told us that we could enter into the quarry itself.

An uneven landscape with machinery.
Basalt quarry 4 km north in Ban Lung, Ratanakiri province, Cambodia. Image: Paula Piilonen © Canadian Museum of Nature

At the bottom of the quarry, we made a startling discovery. Although the larger blocks are drilled off and pushed to the bottom of the quarry (explosives are not allowed here), the bulk of the work to reduce the boulders to smaller fragments (about 30 cm to 60 cm) was being done BY HAND. Workers (in flip flops) stand in the rock piles and split boulders using only a large sledgehammer. A full shift of this manual labour must be back-breaking.

The smaller fragments are then loaded into a dump truck and fed into the crushers at the top of the quarry, where they are reduced to road fill (15 cm to 30 cm).

Images: A man uses a sledgehammer among piles of rocks; machines make piles of crushed rock.
Left: A quarry worker splits basalt, his only tool a sledgehammer. The fruit of his labour is further crushed by machines, at right. Images: Paula Piilonen © Canadian Museum of Nature

The quarry itself was an amazing experience for a geologist: a textbook-quality volcanic section consisting of three distinct basalt flows. Having access to the quarry wall to study (and sample) this section adds important information to our study of the basalts in the region. Nowhere else can multiple, fresh flows be observed in a single locality.

Images: A man stands beside a rock wall; lines demarcating three basalt layers have been applied to a photo (Top: Vesicular columnar 1.5 m, Middle: massive columnar 40 cm wide, Bottom: massive columnar 1.5 m wide).
Glenn Poirier examines a large (1.5 m wide) basalt column at the bottom of the quarry. Three distinct basalt flows can be identified. Images: Paula Piilonen © Canadian Museum of Nature

We were able to collect 15 kg of rock and leave the quarry satisfied with an excellent morning of work.