Hey Chud
Look up biscuit stone/ discodial some are cupped and some resemble a biscuit like yours. I have found several. One theory is they were used as targets and are in the game stone category. Rock could also be right pecking stones are similar. If a pecking stone you will see concentrated wear some pecking stones also are cupped for the thumb to fit. Looks like you are on the right track chances are you are at the right spot as you learn the different types of artifacts from your area you will start to see them. This is an Adze from our area it is made from a fine grained granite you can see the pecking is still evident after the grinding process look at the nicely rounded bit.