Dims: 1.65x0.71x0.63" (4.2x1.8x1.6cm)
Wt: 0.62oz (17.6g)
Fresnillo, Zacatecas, Mexico
This is a very nice specimen of polybasite (or pearcite, or some intermediate member of this solution series). Most of the mass in the specimen is silvery acanthite (pseudomorphed after argentite). The polybasite occurs as a dozen or more flat plates intergrown with the acanthite. These plates are noticably more "black" than silver, and show red fire. The thinnest of them are actually translucent - you can see a red glow through them, although a loupe is needed to see this. Some of the plates have a hexagonal outline, although most are simply irregular. There are also a dozen or so crystals of a colorless transparent mineral, which has a hexagonal shape but an very complex stepped growth pattern / termination. I thought "quartz" before I used the loupe to examine the mineral. I have seen aquamarines with similar texture and habit, but I don't honestly have any real idea as to what this is.