Proustite, Gypsum
Miniature, 4.4 x 3.7 x 2.8 cm
Platosa Mine, Bermejillo, Durango, Mexico
From a small pocket collected in 2004, this is an unusual specimen in several regards. Firstly, it is just a very rich proustite for a Mexican locale (though other silver minerals are common enough for Mexico, proustite surely is not). Secondly, it is the only one I have personally seen on selenite, both including it and growing upon a smothered selenite crystal or mass. All in all, a most unusual specimen, that happens also to be red and sparkly, and quite gemmy, when backlit. This is a unique piece in my experience.The following information is from Peter Megaw:Gentlemen: I do indeed know this property, being (modesty aside) credited with its discovery. It is perhaps more accurate to say that there are 2 pieces to Platosa. The historic mine, where oxidized mineralization daylighted, produced quantities of gypsum/selenite crystals, many with distinctive black phantoms and/or encrustrations of hydrozincite (and rare but lovely examples studded with blue rice-grain smithsonites). Mike New brought out most of these and I got there when the property owner asked Mike if he knew anyone who might be interested in exploring for more of the high-grade silver-lead-zinc ore his father used to mine. Our exploration was very successful and we found the unoxidized, faulted continuation of the orebodies worked in the historic mine with stellar silver-lead-zinc grades. The "new" mine was put into production in 2005 and by mid-2006 we had reached the #5 Manto where silver grades reached 2.5%! It was there that small pods of proustite were found...both as free-standing crystals and frozen in water-clear gypsum. Most of the larger crystals came from the gypsum zone and the gypsum was leached off. The #5 Manto is now exhausted, except for some corners, and only trace amounts of proustite have been found in the other bodies. The ore contains significant amounts of exceedingly fine-grained native silver in massive acanthite, but I have never seen anything I would call a native silver specimen from here. Perhaps someone is cooking them?Overall, outside of the 5 Manto, Platosa is remarkable for its lack of significant voids in the ore proper...especially in comparison to its cousins like Santa Eulalia, Naica, San Martin, etc. There aren't really any decent pockets with calcite or fluorite, let along sulfides bigger than a few mm. This can/will probably change, I can perhaps tell you more after my upcoming visit.However, there are caverns lined with large (2 m) gypsum crystals here and there in the mine...they are a real pain since they are full of water and can flood the mine in minutes. Still working on getting some of these out...unlike Naica, they are heavily included so they are not all that attractive.