Pumpellyite var. Chlorastrolite

specimen number:
2062075

location:
Isle Royale Mine, Houghton Co., Michigan, USA

description:

A polished example of radiating crystallized pumpellyite, this known as chlorastrolite. This is an exceptional example that at one time was part of the collection of Donald Gabriel at the Seaman Mineral Museum at Michigan Tech University. This was collected by Gabriel in the 1930s, mined directly from hard rock and not a beach pebble or tumbled stone.

Chlorastrolite is a rare variety of the mineral pumpellyite that occurs in cavities within basalt lava flows of the Keweenaw Peninsula in northern Michigan. It is best known as the official state gem of Michigan and is commonly called the Lake Superior stone. The mineral typically forms rounded nodules that, when cut and polished, display a distinctive radiating green pattern that resembles a turtle shell, caused by its fibrous internal structure. Most chlorastrolite is found along the shores and underwater areas of Isle Royale and the Keweenaw Peninsula, where erosion of the basalt has released the nodules. This one however was mined directly from hard rock and was not a beach pebble.

Donald Gabriel was a mineral collector associated with Michigan Technological University and the A. E. Seaman Mineral Museum, where his collection became part of the museums holdings. His specimens are known for good documentation and include material from Michigan and other classic localities. The Gabriel collection was incorporated into the museum in the late 20th century and remains part of its permanent collection.

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