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You will find there is difference between rocks and bricks.

Hard to say. From my experience a lot of these companies just ship in already made material from China as it is much cheaper for them then to quarry and dress their own material.

You could use pogoing to get away.

Use polished convex part of spoon, make few pases on the stone and check for scratches. For simmilar job you could use ols casing from ball bearing but spoon is easier to get. Once scratched can be...

If you do not want to put your blade to it Henk showed me his testing way of unknown rocks. He uses old tea spoon which is realy easy repolish between tests.