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Very hard rock or mineral - has me stumped.

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I hope I have enough information (not just a picture) for speculation on what it could be . . .

It is very hard. I ran through 7 days of a vibrating polisher course grind grit with agate, etc - polished the agates and barely touched this stone. I attempted to grind it with an old lapidary wheel I have, in five minutes it ground one little spot (pic 00_stone3.jpg shows the spot) and a steel file won't scratch it. It will scratch quartz and agate - neither of those will scratch it.

I found it in snorkeling in Lake Superior near Grand Marais approximately 8 miles from Agate Beach.

If I had to describe the color I would say ox blood red.

Weighs 120g and displaced approximately 50ml water (I was using a large measuring cup so not extremely accurate). I come up with a density of approximately 2.4 (am I doing that right??).

Here is a picture of the stone:


Thanks for looking!

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I had considered granite initially MOHS 7 - but then when it wouldn't polish when agate and quartz did I thought it couldn't be granite. It will round a sharp quartz point in a single swipe.

I am new to hard stone. Is there some reason granite in particular won't polish with items of the same hardness??

I picked this stone up because it was rough and every other stone I was looking at was worn smooth by Lake Superior.

Thanks. I'm here to learn.

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Interesting rock and very hard to tell exactly from your photo, can you cut the end off? When you say it will not take a polish is it because the surface stays rough or chips away? Usually when a stone will not polish in the tumbler like you say it is either too soft or fragile.

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