Please, PLEASE! Don't break this!
A streak test does not harm the rock. It just scrapes off a little of it, and may give an accurate identification of the rock itself.
It may be sandstone. It might even be a nodule.
But it also might be an early goddess icon, like those found in Europe.
I don't think this is natural. The straight line would have gone completely through the stone in that case.
I do think it might have a rudimentary face carved on it. Might even have other features if the surface of the rock is carefully cleaned. Personally, I'd take it to an archeaolgist first, just to make sure it isn't ancient and/or man-made. You can always crack it open afterwards, if you want. But it's just as likely the stone will shatter if its sandstone, as has been suggested.
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