Rock face showing embedded pyrite crystals

by David Rusterholz

David contacted me in the summer of 2015, to ask about going to Navajun to collect. He is an avid collector, Chemistry Professor Emeritus at the University of Wisconsin-River Falls, and President of the St. Croix Rockhounds of Stillwater, MN. David asked a bunch of questions about what it is like collecting at Navajun. Apparently I answered his questions satisfactorily because in late November he and his wife Becky Kleager made the pilgrimage to Navajun, Spain to do some pyrite collecting at Mina Ampliación a Victoria. Below is his report. -Eric


Sphalerite cut gemstones


Sphalerite gem rough

Sphalerite is a zinc sulphide mineral (Zn,Fe)S that is the chief ore of zinc. While common as massive ore and crystals, gem quality rough is extremely rare. Gems that display flashes of light are prized for their exceptional fire, which is the result of the dispersion of white light into the separate spectral colors. Top grade gem sphalerite specimens exhibit a dispersion value of 0.156, which is three and a half times higher than that of diamonds, at 0.044. In measurements of how light passes through sphalerite, it has a refractive index of 2.37, just slightly less than diamond, at 2.42. Sphalerite is a fairly dense stone, with a specific gravity of around 4.0, so even small cut stones will weigh a comparatively high number of carats for their size.

by Eric Greene

INTRODUCTION

Mina Ampliación a Victoria is a pyrite deposit about 4 kilometers north-northwest of the tiny village of Navajún, in the Cervera district in La Rioja province, Spain. The surrounding area forms the headwaters of the Barranco de la Nava in the Sierra de Alcarama foothills of the Iberian Range. The deposit was discovered in 1965, and, through the years, pyrite from Navajún has been appreciated by and highly sought after by mineral collectors for its unique, highly aesthetic, exquisitely sharp, brightly lustrous, near-perfect single cubic crystals, clusters of interpenetrating crystals, and crystals embedded in matrix. Arguably the finest cubic pyrite crystals in the world come from Navajún (not Logrono, as they are sometimes mislabeled). The degree of perfection of these crystals causes many neophytes to exclaim in amazement and ask if they are manmade. Because of its beauty and perfection, Navajún pyrite has become the icon of Spanish mineralogy since its discovery.


by Eric S. Greene

Having the chance to collect pyrite at Navajún, Spain has been #1 on my bucket list since I first saw specimens from Mina Ampliación a Victoria. Now, after a buying trip to Sainte-Marie-aux-Mines in France, my dream was about to come true. It was the 4th of July. My wife Jeanne and I were celebrating America's Independence Day by visiting the Guggenheim Museum in Bilbao, then heading south to Navajún to meet mine owner Pedro Ansorena Conde and dig for pyrite. The drive from Bilbao takes about 3½ hours on a superhighway that passes over and around rolling hills and mountains studded with state-of-the-art windmills and field after field of wine grapes, wheat and hops. The last 40 km of the trip takes over an hour because the road winds through small villages and up, down and around hairpin turns on the way to our destination.