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Rare Silver Mineral Discovered in Princeton Mineral Collection

Aguilarite under a microscope.

Aguilarite under a microscope. Photo by Christopher Holl.


A rare and long-sought-after silver mineral has been discovered in the Gem and Mineral Collection of the Department of Geosciences

Luca Bindi, Professor of Mineralogy and Crystallography at the Department of Earth Sciences of the University of Florence, Italy, discovered the sample of aguilarite (Ag4SeS) in the collection during an autumn 2012 visit to Princeton. Aguilarite is an extremely rare mineral, intermediate in composition between two more common minerals, acanthite and naumannite.  This group of minerals represents an important ore of silver in Mexico, but the structure of aquilarite remained unknown, as suitable samples for study could not be located. Using the Princeton specimen, Prof. Bindi and his colleagues determined the crystal structure of aguilarite for the first time, showing it to be identical to acanthite and not naumannite as previously assumed. 

This discovery also holds ramifications for research in semiconducting materials and optics.  The Princeton specimen is from the type locality (the source of the samples from which the first scientific descriptions were made), the San Carlos Mine, Guanajuato, Mexico and was probably collected during or prior to the 1920s.  The discovery highlights the continued importance of mineral collections in modern geoscience research.

Reference:  Bindi, L. & Pingitore, N.E. (2013) On the symmetry and crystal structure of aguilarite, Ag4SeS. Mineralogical Magazine, 77, 21-31.