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How amethyst cathedrals form
(St. Croix Rockhounds, Stillwater, MN, 2007)
Why pyrite crystals have different shapes
(St. Croix Rockhounds, Stillwater, MN, 1994)
How fast can crystals grow?
(St. Croix Rockhounds, Stillwater, MN, 2004)
Why do such large crystals form in pegmatites?
(St. Croix Rockhounds, Stillwater, MN, 1987)