John Betts - Fine Minerals > Home Page > Minerals For Sale > Minerals For Sale From Milpillas Mine, Mexico > Pyrite coated with Chalcocite |
UP-TO-DATE INFORMATION ABOUT COATED PYRITE CRYSTALS FROM MILPILLAS MINE, MEXICO
There has been a series of errors in identification
of the gray-metallic-coated pyrite crystals from the Milpillas Mine,
Mexico. Here is a chronology of the evolution of misidentifications:
These events are an example of how one wholesaler, in a rush to sell a new find, failed to wait for proper testing, and propagated false information throughout the mineral community. A similar misidentification occurred with the "ajoite" from the Luputo Mine which was actually chrysocolla. I understand the rush to announce new finds, and I understand that EDS is fast and easy. But EDS is not a good test for all cases. When results are not definitive, it is wrong for the wholesaler to "decide" what they should be labeled. As dealers and collectors, it pays to ask questions regarding testing and identification. Finally, it is noted that chalcocite coating on pyrite is known from several other localities, including the Burra Burra Copper Mine, South Australia, Australia; Chino Mine, Santa Rita District, Grant County, New Mexico; and Ducktown Mine, County, Tennessee in the USA. The latter were sold as "ducktownite" which were later identified as chalcocite-coated pyrite. The varietal name ducktownite still persists to describe pyrite crystals coated with gray-metallic chalcocite. SPECIAL NOTE: The pyrite crystals at the Milpillas Mine were fractured after they crystallized and the crystal fragments were frozen in the white dickite-rich matrix, with thin fractures filled with matrix. John White in the recent Rocks & Minerals magazine describes this as "disjoined" crystals. But the chalcocite coating is on all surfaces of the pyrite crystals, including the fractured surfaces. That means: 1.) pyrite crystallized; 2.) the pyrite crystals fractured and were frozen in matrix; 3.) the chalcocite coating formed on all surfaces of the pyrite at the end
PYRITE WITH CHALCOCITE COATING FROM MILPILLAS MINE, MEXICO
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