Prehnite

specimen number:
2062377

location:
Isle Royale, Michigan, USA

description:
A pink and colorless section of massive renowned, this polished on one face. Collected in 1966.

Isle Royale in Michigan is characterized by a geologic syncline formed about one billion years ago during the Midcontinent Rift, consisting primarily of ancient basaltic lava flows and conglomerate layers shaped later by glacial activity. Along the island beaches, visitors can find smooth pebbles of prehnite, an abundant secondary mineral that often forms pink or green amygdule fillings in the volcanic rocks, colored internally by tiny native copper inclusions.

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