Imagine miles of freshly turned red earth everywhere you look. Above, a sky so blue it hurts the eye. In the centre of this colour-saturated landscape is a small area that’s cordoned off and heavily guarded, although it looks no different from the spot you’re standing on. But get closer and you’ll see a pinkish speck or two on the ground. Then another one, and two more over there. Like new stars appearing the longer you stare at a night sky, the gems sparkle in the mud like so many badly kept secrets. Welcome to Montepuez, the largest ruby deposit in the world.

Wearing hard hats and reflective vests—although this is a flat mine and no threat to claustrophobes— we walked about like kids on Christmas morning, these beauties teeming underfoot. A few guards circulated among us holding red tins into which we’d reluctantly drop the stones we found. We saw them later at the sorting house run by the British gemstone company Gemfields, but the thrill of chancing upon rubies in the raw is unmatched. It’s how you’d imagine geologist Paul Allan felt when he first got to this corner of the Cabo Delgado province in northeastern Mozambique, back in 2009.

Allan, who worked in diamond mines before this, describes the experience of seeing precious stones almost casually strewn about as “amazing and humbling”. What he’s referring to, and where we went prospecting earlier that day, is a secondary mine owned by Gemfields.