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Generalcandy stripe lakers found in situ north shore lake superior

16th Sep 2019 06:58 BSTAshley Wise

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I bought property in Tofte and to my complete surprise found in situ traditional red/white candy striipe lake superior agates in situ in a small cave in ledge rock.

This has been a holy grail of mine. Every time I got up to the north shore I'm in search of agates in matrix. I've presumed they were all long eroded out of the upper 5 miles of volcanic basalts already eroded away by glaciers in the last 100k years

I've found of thompsonites (and 15+ miles away from grand marais, despite the claim they are only found in a 1 mile region), but never lakers before.

This area appears to be in NSU under NSM (north shore stratified rock) according to geology maps. But it looks pretty basaltic, not sandstone. The grand marais artist point has a columnar basalt over a planar basalt (but maybe it's planar sandstone?) And this looks similar, a vary planar, easily erodeable zone of basalt (an upper gas bubble filled zone of a basalt flow) under a more structurally stable basalt.

What is interesting is that most of this zone is filled with traditional feldspar/quartz. Most vesicular voids appear coated with a non-layered red mineral, and filled with a prismatic quarts or calcite mineral (probably quarts since agates are present). But the larger football-shaped voids appear to be red lined with large crystalline shaped quarts) no agate banding)

Well anyway, let the pictures do the talking.

Ok, Please someone explain to me how to post pictures in this new forum

16th Sep 2019 13:20 BSTAshley Wise

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The previous water-level agate was around the size of a golfball. These others were marble-sized.

16th Sep 2019 13:21 BSTAshley Wise

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Another

16th Sep 2019 13:22 BSTAshley Wise

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A nice amethyst core. I'd found a larger golf-ball sized one of these in a stream nearby years ago. I didn't look particularly glacially tumbled, so now I think it actually came out locally up-stream.

16th Sep 2019 13:23 BSTAshley Wise

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Here's the inside of the cave. You can see two of the agates, mid-upper and upper-right.

16th Sep 2019 13:26 BSTAshley Wise

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And the outside

17th Sep 2019 05:15 BSTMatt Neuzil Expert

I spy lots of little agates! You're very lucky to have that so close to you

17th Sep 2019 09:55 BSTFranz Bernhard Expert

Very spectacular and nice finds!
I am wondering about the origin of this "cave". It does not look natural to me, but what do you think about its origin?
Franz Bernhard

17th Sep 2019 02:44 BSTPaul Brandes Manager

Congrats on your finds, Ashley!

Much of the basalt you're finding these in are related to the flows found on the Keweenaw Peninsula in Michigan which are also known to contain agates. In addition, agates in-situ can still be found on the Keweenaw in the Lake Shore Traps. Another Mindater (Larry Maltby) has found several very beautiful agates in this formation.

18th Sep 2019 13:57 BSTAshley Wise

The Keweenaw agates are completely different from MN lakers. I have many Keweenaw specimens too, I 've love their "ruined" look and soft salmon colors, and got most from people in the UP who acquired them directly from bedrock in their property.

But I'm specifically referring to the agate type most Minnesotans perceive as the "standard" laker, the red and white candystripe, or red-shelled quarts centered type, or the red banded type.

This is the type of agate, with bright red bands, I've yet to ever find in-situ on the north shore, until last weekend. It's a completely different type of agate from the Keweenaw agate.

I've seen other types of agates in-situ. There's the white and pink solid type around two harbors, isle royal "paradise beach" paint type.

And of course the non-agate thompsonites.

What's interesting is I've always figured the red&white lakers are probably from higher flows long eroded, since this is the most common form found way south all the way through anoka/maple grove/elk river etc. And their lack of occurance on the north shore. And this particular flow I found these in is near the very youngest/highest flows on the north shore.

What else is interesting is I believe this flow is the one right above the thompsonite flow, and I'd been told on here previously that zeolites prevent agate formation, so there shouldn't be agates above thompsonites. I've found gem thompsonites and banded zeolites both west and east of this in lower strata.

 
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