The Blackbird Mine has arguably produced America's finest ludlamite specimens. These textbook crystals are considered a benchmark for the species, still. I am told that most would have come out prior to 1970, and few are seen for sale today (I certainly buy all I can, especially when as displayable as this one). Stacked, glassy and gemmy, bright green crystals of ludlamite to 6 mm across are aesthetically emplaced on matrix. An aesthetic miniature specimen, for any collection of USA minerals! A slight coating of siderite is still on these crystals, left on for authenticity. It could probably be removed by careful cleaning. Wikipedia: Mining for gold started in 1893 and the cobalt content was recognized in 1901. The mine produced copper and cobalt between 1902 and 1968.