YES, there is a stone known as the "Green Turtle Stone" It was not made up by some kids to cause a sensation.
In 1972, Chlorastrolite became the official State Gemstone for Michigan. Chlorastrolite is a beautiful green mineral with a chatlyant "turtle-back" pattern. Don't feel too bad if you are unfamiliar with the name. First of all, it is quite uncommon. Gem varieties are only found in Michigan. Secondly, there has been some confusion over the correct name as well as its true identity. It has been considered to be a Zoisite, a variety of Prehnite and a variety of Thomsonite. It has been called lotrite, kearsargeite, zonochlorite, lintonite, pumpellyite, chlorastrolite and greenstone. After much research, the IMA has ruled that the gem we are talking about is to be called "Chlorastrolite," - Michigan collectors still call it by the common name, "greenstone" or "Turtle Stone".
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Chlorastrolite occurs in the basalt layer deep under the Keweenaw Peninsula. When Isle Royale was formed off-shore from Keweenaw by an upheaval of the bedrock under Lake Superior, some of this material was brought to the surface. This tilting of the bedrock exposed the greenstone-bearing basalt. Wave action erodes the greenstones free and they may be found as beach gravel on the Isle. For many years this was thought to be the only source of the gem. When first offered in jewelry by the NewYork fashion stores in the 1890s, they were referred to as "Isle Royale Greenstones." To this day, many persons fail to realize that much of the Chlorastrolite occurred under the Keweenaw Peninsula and was discarded on mine dumps by the copper miners when they tunneled to the copper. The mines are not operating now and new material is not being brought to the surface, but the greenstones are usually overlooked by the rockhounds searching for copper. You can find gem-quality Chlorastrolite at the mine dumps if you look carefully. Greenstones have been found at most of the mines at Keweenaw; however, some mines produce better greenstones than others. The Central Mine, located just off US 41 north of Calumet, has been the most recent source of some of the largest greenstones.
Chlorastrolite occurs in the basalt layer deep under the Keweenaw Peninsula. When Isle Royale was formed off-shore from Keweenaw by an upheaval of the bedrock under Lake Superior, some of this material was brought to the surface. This tilting of the bedrock exposed the greenstone-bearing basalt. Wave action erodes the greenstones free and they may be found as beach gravel on the Isle. For many years this was thought to be the only source of the gem. When first offered in jewelry by the NewYork fashion stores in the 1890s, they were referred to as "Isle Royale Greenstones." To this day, many persons fail to realize that much of the Chlorastrolite occurred under the Keweenaw Peninsula and was discarded on mine dumps by the copper miners when they tunneled to the copper. The mines are not operating now and new material is not being brought to the surface, but the greenstones are usually overlooked by the rockhounds searching for copper. You can find gem-quality Chlorastrolite at the mine dumps if you look carefully. Greenstones have been found at most of the mines at Keweenaw; however, some mines produce better greenstones than others. The Central Mine, located just off US 41 north of Calumet, has been the most recent source of some of the largest greenstones.
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So as not to raise to much confusion or start an arguement over what is Michigan's selection, one needs to also know that Michigan's State Stone, which is much better known, especially to Lapidarist, is 'The Petoskey Stone'. Petoskey Stones are masses of fossil colony coral, Hexagonaria Percarinata. They occur abundantly in Devonian reef limestones of the Traverse Group in the northern part of the Southern Peninsula of Michigan. The Devonian Period was about 350 million years ago. Coral groups weathered out of the limestone were widely scattered by Pleistocene glacial action. They are readily found on beaches and in gravel deposits as pebbles and cobbles rounded by erosion. Petoskey is the English adaptation of either "Be-dos-e-gay" or "Petosegay," an Ottawa Indian word and variant meaning "sun rays of the dawn." .
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