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Disrupted agate? From Lake Superior

Posted by Moe Hawk  
Moe Hawk
Disrupted agate? From Lake Superior
February 28, 2012 10:55PM
I found this near Silver City, Michigan on the shore of Lake Superior. It definitely has some banding but not concentric. There are pieces of breccia inside. I believe the matrix is basalt, but it is reddish brown in color much like sandstone. There are two different crystal types I believe; calcite and stained quartz maybe? There is also a small amount of bright green something exposed at the surface. Any input is greatly appreciated!
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avatar Re: Disrupted agate? From Lake Superior
February 28, 2012 11:34PM
    
It is quartz, and those blocky masses may be calcite. poor some vinegar on it and see if it fizzes. if it does, its calcite.

-Rowan Lytle

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avatar Re: Disrupted agate? From Lake Superior
February 28, 2012 11:57PM
Moe,
What you have is something called a Brecciated Agate, also sometimes called a disrupted agate. They form when the original agate got partially crushed, breaking up the banding and scattering them around within the vesicle or rock itself. It is thought that any remaining silica solution in the rock then filled in the spaces and healed the rock to form one solid specimen again. The drusy quartz likely formed during the re-healing stage.

I don’t see any calcite in the specimen; it appears to be all quartz. The red colour reminds me more of rhyolite, which is also a common matrix of agate, although basalt can also have a red tint as well.

Neat specimen at any rate!! thumbs up
Raymond Hietapakka
Re: Disrupted agate? From Lake Superior
March 01, 2012 01:46PM
Looks identical to some seam agate found near the Current River in Thunder Bay, Ontario...found in a single 1"-6" wide horizontal band at the unconformity of a Logan diabase sill, and the underlying Gunflint Formation rock underneath. Some unique pyrite-encrusted amethyst here also.
Moe Hawk
Re: Disrupted agate? From Lake Superior
March 02, 2012 12:26AM
Thanks for the input everyone! Didn't have any vinegar but pickle juice didn't produce any bubbling haha. The mystery crystals are indeed block like and have fractures(?) that are rhombus shaped.
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