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145:. Isle Royale is a National Park, and so it is illegal to collect specimens there. It is difficult to identify an unpolished pebble of chlorastrolite. Most gem quality chlorastrolite stones are very small, and it is rare to find one that is larger than a half inch. The largest gem quality stone is in the Smithsonian Museum and measures 1.5 by 3 inches.
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Arguably the rarest gemstone in the world and one of the most valuable
American gemstones. The gem quality specimens are typically found on Isle Royale, a large island off the Northeastern tip of Minnesota. a
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It was first described from Isle Royale, Lake
Superior by C. T. Jackson and J. D. Whitney in 1847. Chlorastrolite, also known as greenstone, is the official
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is a misnomer sometimes given rounded masses of chlorastrolite within or weathered out of amygdaloidal cavities, especially those from the area around
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is a name sometimes given because of the overall pattern, particularly in polished pieces, which roughly resembles that of a turtle shell.
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The
Geologic Story of Isle Royale National Park, USGS Bulletin 1309
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105:. Chlorastrolite was once thought to be an impure variety of
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Bluish-green sorosilicate, state gemstone of
Michigan
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399:The geologic story of Isle Royale National Park
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313:adding citations to reliable sources
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135:Upper Peninsula of Michigan
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526:Isle Royale National Park
397:Norman King Huber, 1979,
391:Gemrocks - chlorastrolite
262:Michigan's State Gemstone
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273:Huber, N. King (1975).
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521:Symbols of Michigan
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200:Turtle back
185:Isle Royale
160:Other names
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117:Occurrences
36:pumpellyite
475:Categories
335:newspapers
247:References
194:greenstone
187:greenstone
180:Greenstone
123:amygdaloid
111:thomsonite
506:Gemstones
150:state gem
49:(Mg,Fe)Al
32:chatoyant
214:Scotland
170:Michigan
154:Michigan
107:prehnite
349:scholar
232:Ontario
133:of the
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236:Canada
206:Uigite
127:basalt
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