I have quite a few mystery stones which I've posted in another thread, but there's one in particular that I would really like to know more about as it's a top quality stone, and I think very pretty.
This is a very hard and fine slate, and excellent finisher. Merely from the colour I guess it's probably Welsh but I've no idea, the green-blue appearance is more apparent when wet, when dry the stone looks more grey.
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It has some weird and pretty patterns down the side too.
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This picture shows it above a Glanrafon; the two stones are similar-ish but not the same, the mystery stone is probably marginally harder and finer. It's not an Idwal either.
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I only know of one other person who has what I'm certain is the same stone, so they're not that common. But would be very keen to hear if anyone knew anything about it...