A bluestone (argillaceous sandstone) that is quarried extensively near the Hudson River in New York for use as flagstone. Very hard sandstone. Difficult to tool. Takes a polish.
Hudson River Bluestone
NOTE: Quarry locations are approximate.
Grippy Ln.12193 Westerlo , New York
United States42° 33' 35.64" N, 74° 4' 21.72" W
New York US