Exquisite group of sharp metallic crystals to 7 mm on matrix from the classic Mexican location for silver minerals, Guanajuanto. These crystals appear to have been deposited onto argentite crystals which formed earlier and were likely coated with some microcrystalline silver mineral. Some of the earlier deposited argentite has formed very interesting washboard crystal groups which give the piece an unusual look. Ex. Earl Calvert collection circa 1930s-1960s probably.