Windy and a bit of rain. Fence has been put up around the north east side of the field, closing off the road and the strip of grass north of the construction site. Talked to a couple of construction workers and got access to the field through an opening in the north east corner and walked down the new road to the western part of the field. Collected some soil from a big pile remaining from the ground work, and in the grass infront of the pile I found a very peculiar rock. As long as a forearm, the rock seemed to be a mix of flint, glass and plastic. Asked a construction worker if he knew what it was, but I had difficulty understanding his Dutch. He said something about it coming from deep down and that it was not natural and a kind of waste.