R This is a great example of the two minerals with the same chemical composition but very different physical properties on the same specimen. Polymorphs! Xanthoconite occurs on this specimen as dark orange-yellow, chisel-shaped crystals. Extremely well formed. The proustite occurs as ruby-red, terminated prisms and sprays, sometimes twinned, all over the specimen. There are many more proustites than xanthoconite. The matrix is corroded, argentiferous galena with small, sharp arsenopyrite crystals sprinkled here and there. Really great example!