Pumpellyite set

specimen number:
1791324

location:
Isle Royale, Michigan, USA

description:
A set of green pumpellyite specimens, this the variety known as chlorastrolite. Some are tumble polished. Size provided for the largest example.

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.

Chlorastrolite is a variety of the mineral pumpellyite, commonly known as the Isle Royale greenstone or Michigan's state gemstone. It typically forms within the vesicles of ancient basaltic lava flows and is famous for its distinct green color and unique starburst or turtleback mosaic pattern caused by radiating fibrous crystals. Because of its attractive chatoyancy and rarity, small polished pieces are frequently collected and used in jewelry, though large specimens remain exceptionally scarce.

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