Meetiyagoda moonstone

Blue moonstone is one of the few gemstones with an address rather than a range, and the address is a village near Ambalangoda in southwestern Sri Lanka.

The stone is feldspar. Alternating microscopic layers of two feldspars, orthoclase and albite, unmixed as the crystal cooled, scatter light between them and throw a soft glow that floats over the surface as you tilt it. The effect is adularescence, and the finest expression of it is a near-colourless transparent body with a strong blue sheen sitting on top. That combination is what Meetiyagoda is known for and what puts Ceylon moonstone at the top of the market.

The geology is a pegmatite that has rotted. Chemical weathering in a tropical climate has broken the feldspar-rich rock down to kaolin clay, and the tough moonstone crystals survive in the soft matrix, so miners are digging clay rather than blasting rock. The deposit was found in 1906 during agricultural work, which is an unglamorous origin for a stone that has dominated the local trade ever since.

The mining is what makes it worth a visit. Miners sink narrow pits, sometimes down to twelve metres, then drive branching tunnels off the bottom, shored with timber, and haul the clay up by hand and winch. It is small-scale, family-scale work, and several of the pits around Meetiyagoda take visitors, show you the shaft and the washing, and sell out of the attached workshop.

Go with the expectation of watching rather than digging. This is a working private deposit and the pits belong to the families who sank them. Buying a stone at the pit head from the people who dug it is about as short as a gem supply chain ever gets.