I know standards must be different for early copper, but with corrosion that deep, I don't see how it could grade cleanly. Not my field, though; I'll look forward to more knowledgeable opinions.
Yes it is a crosslet 4 (as most of them are). The cud above LIBE tells me it is a C-8 Die stage VII. C-8 is one of the four Spiked chin varieties, unfortunately it is one of the common ones, but the late die stage makes it interesting. I would say it is NOT worth slabbing.
