.	Dwarves' Earth Treasures Online Museum: Mandan Datolites Mandan Pit just east of Delaware, Keweenaw CO., Michigan	.

 .     Mandan Pit is a gravel pit full of rocks and sand that were carried from nearby sources and deposited by ancient glaciers. Datolites, "float copper" and few other interesting rocks can be found there assuming that you're able to beat anyone to them that is. I hadn't had any good luck with that site so far. Most datolites found there are heavily weathered (bleached), and I found one that just crumbles away easily. But there are some datolites found with colorful centers still intact.. There was a rumor of purple datolite being found there.
Was mislabelled as "Drexel Mine" so anyone have to be carefull when buying any datolites from anyone.