to me it looks like a broken piece of columnar basalt. It does almost look like it has sharpening marks, but like mentioned above, tools like an axe were usually churt or obsidian, not basalt. Basalt is very hard, but tends to shatter or fracture. I have seen lots of sharp, broken pieces of basalt. The area it was found could tell you alot too... It looks like it could definitely chop something down.