Ferrokesterite (twin) (exceptionally rare)

Item Description

The San Jose Mine in Oruro, Bolivia has been a source of minerals and metal since the time of the Spanish conquistadors. The native people in Bolivia were certainly mining silver in this area for many years before any Europeans even arrived in South America. In 2004 there was a tremendous discovery of the world's finest crystals of Andorite at the San Jose Mine, but along with those crystals came the finest specimens of Ferrokesterite. At first, these specimens were labeled as Stannite, but through analysis by Bob Downs at the University of Arizona, they were confirmed as the finest known examples of the incredibly rare dimorph Ferrokesterite in existence. Before the Bolivian pieces were found, the best known examples were tiny 1-2 mm "smears" on matrix from the Cligga Mine in Cornwall, England, which is the type locality for the species. The Bolivian specimens are worlds better than anything from Cornwall. You'll notice on this specimen that the crystals are large for the species, and have formed eye-catching penetration twins. This thumbnail sized specimen features well-formed, tetragonal / octahedral penetration twinned crystals of Ferrokesterite with a lovely brassy patina free of matrix. Several acicular silvery-grey Zinkenite crystals can be seen on the piece as well for a nice touch. This is a really super example of an incredibly rare mineral, and considering that nothing has come out of the ground for many years, we probably will never see them again. If you'd like to read the FULL STORY on this history these specimens, please read the article by Brian Kosnar on his website at www.minclassics.com/ferrokesterite.html .