Green Stones from Lake Michigan--NOT Greenstone

[amelissa]

I've been picking these up on the shore of Lake Michigan (Chicago specifically) but I'm having trouble identifying them, since searches for "lake michigan green stone" and variations thereof only turn up pages about chlorastrolite, which I'm pretty sure they aren't. They're a soft grey-green color, but in places where they're pitted or areas seem to have been worn away they're a darker grey, as if the green is just an outer layer. Any idea what they might be?

 

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[uglymailman]

There is a thread here called "Got a rock you want identified" or something close to that. Do a search & it should come up. Several people there can help you. Good luck.

 

[DDancer]

There are a variety of copper minerals in your region so I can speculate that you may have a very low grade form of Chrysoprase. It definitely looks silicate with some large compacted crystals. Chysoprase is usually a Chalcedony form of quartz with no real crystal definition but when quartz is on the border of large and small crystalline matrix it can pick up the copper coloration. My thoughts.

 

[Moesia]

Brake one up and post a picture of the fresh surface. Can you scratch it with a knife? Probably quartz of some sort.