gneiss

Alternating light and dark BANDS that you can trace across the whole stone. Granite is speckled with no grain; gneiss has a grain.

The bands are not sediment layers. They are minerals that separated under enormous pressure, which is why they can fold and swirl.

Michigan beach gneiss comes from two very different places. The Archean stuff out of the Superior Province runs 2.5 to 3.6 billion years, and Michigan's own Watersmeet gneiss in the western UP is about 3.56. The Grenville gneiss from eastern Ontario is around a billion, and that is the one that really is the root of a vanished mountain.