I called Maidstone Museum, and went back yesterday to try to get photos - not easy facing a setting sun - and I brought a sample home with me to drop off on Monday - the flint cortex is usually stained yellow by the sand, but these have a coating, not a stain, that does partially come away with water, but still leaving a dark shadow. Hard to explain really, but I expect someone to at least have a look...and while they're around, I'll drag them up the road to the edges of the golf course and show them two round barrows that nobody seems to have noticed before...quite exciting really, as there is an unploughed wood to the west of the hearth and a lot of the quarry has never been dug out, so there is plenty of room to explore for more.