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Dwarves' Earth Treasures Online Museum:
Isle Royale Mine Datolites
Isle Royale Mine #6, Houghton, Houghton Co., Michigan
Field-collecting Status:  Private Property, No trespassing!

.    Like the Centennial Mine, the Isle Royale Mine just south of Houghton, produced a small percentage of datolites that are green to turquoise due to the weathering of very minute copper inclusions by ancient brine. The interesting thing about those datolites from Isle Royale mine is that some are like sponges, soaking up water and as a result, their colors intensify. Most datolites from Isle Royale are white and some came with black to gray copper inclusions. Several times, this mine dump had been bulldozed several times and after that any more datolites have not been found lately that I know of.

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datolite
datolite
Turquoise color intensifies when wet. Typical datolites with gray copper inclusions
datolite datolite
Most greenish datolites(without bluish tint)
I have seen so far.
Most greenish datolites(without bluish tint)
I have seen so far.