Kidney Ore

This months subject at the U3A digi camera club is geology. Something I know little about, I've managed to get a few photos when I've been on walks and knew that somewhere at home we had some Kidney Ore, but  as usual you can  never find things when you need  them. Today I was cleaning out the greenhouse when I found a piece. Not a brilliant example but it will be ok for one of my 5 submitted photos.