Sorry if this is the wrong thread but I’m not sure if anyone can help - I’m strugging to upload the image as the file is too large. Gardening and digging I was hitting against what I though was rock, now I know it was metal. I was pulling and twisting on something like a thigh pencil or slim branch until it came away from the piece it was attached to. And planted my shrub! I washed up the prong and it is pretty old metal, with something that looks like white crystallised granules inside. It appears as if there was a blue stamp of letters or numbers on the prong.