It MAY have been used for working leather or maybe something else.
But I cannot see it being used to work with metals.
I'm thinking it would break.
Interesting item for sure though.
I dont think it is volcanic, volcanic specimens will have a visibly porous surcace. I think that I see some evidence of it being a sedimentary specimen. The blue lines on the first picture is where it looks like sedimentary lines, ane the red lines point to where it looks like it was chiseled out of bedrock. The second picture depicts my hypothesis on how it may have naturally formed. The blue water line shows what could have been exposed to flowing water and anything below the blue line was under the bottom soil (the brown lines):