The top of this specimen is an opening in sphalerite-pyrite vein that is lined with small calcite crystals. As well, though, there are many rounded crystals, some actually spheres of acanthite, ps after argentite. Some of the crystals are very sharp and some are as rounded as can be. Some small pyrite crystals, as well. Not radioactive. Very interesting piece from an old, long closed silver-uranium mine.