basalt

Heavy for its size, evenly dark gray-black all the way through, and no layering at all. Shale splits into sheets; slag has bubbles and usually a color in it when you hold it to the light.

Amygdaloidal basalt, the kind with gas pockets filled by later minerals, is the parent rock of half the Keweenaw list. Datolite, thomsonite, greenstone and agate all grew in holes in basalt.

If the holes are smooth, round and roughly hemispherical, you are probably holding an omar instead. Basalt cavities are irregular and often filled in with a mineral. An omar is a fine-grained sedimentary erratic the ice carried more than seven hundred miles from Hudson Bay, and the pits are where concretions weathered out of it. It is not on this chart. It is still a good find.