It is not often that a very old locality produces a gem material previously unrecorded in the literature. Yet the Capillitas mine in Argentina’s Catamarca Province, once mined by the Incas and long known for its fine rhodochrosite stalactites, has yielded two trapiche-like rhodochrosite gemstones, first observed by the author in August 2014.
The stalactite that produced these two slices was reportedly found in the 1980s. The smaller of the two specimens, a 30 mm round weighing 35 ct (figure 1, left), is a symmetrical example of this rhodochrosite’s cogwheel habit. The 40 mm oval, which weighs 56 ct (figure 1, right), was cut from the same stalactite; it is the only other example of this formation the author could locate.
Rhodochrosite from the Capillitas mine typically consists of minute crystalline grains. These two examples, however, are very coarsely crystalline and are quite possibly twinned, which would explain both the unusually large size of these crystals and their obvious symmetry.
Dr. Carl Francis, former curator of the Mineralogical Museum of Harvard University, points out that stalactites of calcite, which are chemically and structurally similar to rhodochrosite, rarely exhibit this type of growth (pers. comm., 2014). The floral pattern of these red gemstones makes them beautiful and incredibly rare.