Thanks so much for that. It makes it that much more interesting to me to know something about it. I also learned that there is a Keweenaw Fault while I was Googling, not that it was involved.

1) The angular (very angular) dark red to brown clasts, probably shale to slate or mudstone, to maybe sandstone if the grains are large enough

I don't think it's sandstone, as there aren't noticeable grains. It was found among sandstone, but it's much harder. Is there a way that I could tell if it were shale or mudstone?

Off-white to light yellow matrix. The white matrix looks to be quartz which is a common form of silica – common in almost every rock. The other option is calcite, but calcite weathers and is usually softer, so soft that large rocks with a pure calcite matrix are far less common than quartz. Without scratching the rock, or the ability to drop dilute amounts or hydrochloric acid on it, I cannot tell if its quartz or calcite, but quarts seems the most reasonable.

What would be the effect? I have HCl available.

I have no idea if this is a common local rock and if it has a local name – like the Petoskey stone as an example.

I spend a bit of time picking through the rocks on that shore every year, and I have never found one like it. I always keep an eye out. I've found a few agates, but never another one of these. I have found Petoskey's before in the LP.