Argentine rhodochrosite, the Inca Rose

A very old mine produced a gem material that had never been recorded in the literature.

That is how GIA opened its 2016 report on trapiche rhodochrosite. The Capillitas mine in Argentina's Catamarca Province was worked by the Incas and has long been known for fine rhodochrosite stalactites, and yet in August 2014 Russell E. Behnke observed two trapiche-like rhodochrosite gemstones from it, a pattern nobody had described in this material before.

The pieces are small and strange. The flower-patterned slice measures 30 millimetres across and weighs 35 carats, and appears to have formed from three crystals intersecting at 60 degrees to each other. A second specimen from the same mine weighs 56 carats and measures 40 millimetres. Both were cut from a single stalactite reportedly found in the 1980s.

Most rhodochrosite in the world is not gem material at all. It is light pink, opaque and often banded, and it goes into beads, cabochons and carvings rather than onto a facetting wheel. Transparent, pink to red, gem-quality single crystals are rare, and it was the Sweet Home mine in Colorado that introduced them.

The Argentine material became widely known in the late 1930s, after a German gemologist found large volumes of it in Catamarca Province, high in the Andes. The name it carries is older than that. In Argentina the use of rhodochrosite goes back to the Incas, who are said to have believed it was the solidified blood of their fallen rulers.

This is a working mine in remote Andean country, not a collecting stop. The way most people meet Capillitas material is as a polished slice with a rose bullseye in the middle of it.