Coarse Beach Grit

I collect coarse beach grit from a remote beach on the North Yorkshire coast, a few miles North of Whitby. The action of the sea has ground all of the grits to a smooth surface. Wave action deposits particles of a similar size together in an area and I just look around until I find the size I want. It contains ironstone, which was historically used for producing iron, sea-shells and all colors of mineral stones I can not identify.