Chilean lapis lazuli

Lapis lazuli is a deep blue metamorphic rock, made mostly of lazurite with pyrite, diopside and calcite, and it has been prized since antiquity. As early as the 7th millennium BC it was mined at Sar-i Sang in Badakhshan, in what is now northeast Afghanistan; it went into the funeral mask of Tutankhamun, and ground into ultramarine it coloured the robes of the Virgin Mary for Titian and Vermeer. Afghanistan is still a major source. The other great one is high in the Chilean Andes, the source the Inca used for carving artefacts and jewellery, and since 1984 lapis has been the national stone of Chile.

The deposit lies in the Coquimbo Region near Ovalle, at about 3,500 metres by the Gemological Institute of America's account, 3,600 by a Chilean one. It is the only extraction site in the country, known as Flor de los Andes. The lapis there formed in limestone baked by contact metamorphism and later altered by fluids that brought in sulfur, which lazurite needs, and the Chilean stone is blue lazurite with wollastonite, calcite, haüyne, diopside and pyrite. The pyrite gives the gold flecks; too much of it, and the stone turns dull and greenish and is worth less. The deeper the blue, the higher the value, and some Chilean material approaches the quality of fine Afghan lapis.

Chilean accounts date the first mapping of the deposit to 1851 and its registration as a mining property to 1894, and in 1899 the Flor de los Andes company built the road that let machinery reach the workings; the GIA dates mining there from 1905. At the turn of the millennium two companies, Las Flores de Los Andes S.A. and Compañía Minera LapisChile S.A., were producing about 150 tonnes a year.

Much of it is worked locally, into fine jewellery, ornaments and building materials such as tabletops and tiles. Chileans call it oro azul, blue gold. For anyone who wants to see how the stone is mined and made into jewellery, the Chilean guide points to the village of Tulahuén.