Ambondromifehy, Madagascar

Sought-after pebbles in limestone crevices

Blue-green sapphires were found near Madagascar's northern tip in 1994, a few years before the famous sapphire rush in Ilakaka to the south. The deposit lies some 50–100 km south of Antsiranana, the port town once called Diego. Sri Lankan traders still use "Diego" as the deposit's nickname, and much of the rough is traded there. The gem-rich gravel sits very shallow, sometimes right on the surface. The best finds come from pockets and crevices a meter or two down in the limestone bedrock, carved by ancient rivers, where dense sapphire pebbles have collected.

Many cutters, ourselves included, consider these the finest teal sapphires in the world. They're typically brighter than blue-green sapphires from Nigeria, Kenya, Ethiopia and Australia. They're light enough in tone that they usually need no heating, which is otherwise common for brightening blue-green sapphires. They're also a touch more saturated than untreated Montana sapphires, and they hold their color better indoors than Tanzanian teals.