This piece is water worn and I believed the notch was intentional as there is clear change in patina. Also shows some pecking on one side in my opinion. If it was something, what would it do?
Purchasing, if possible, the New England artifact guide, as published by the Massachusetts Archaeological Society, and available online, as well as at their Robbins Museum; as well as either the short or expanded edition of the late Jeff Boudreau's guide to New England projectile points, available from the aforementioned sources, would be a good decision moving forward.
Visiting the Robbins Museum would allow you to view examples of virtually every class of artifact found in southern New England. There just is no substitute for viewing as many genuine examples of artifacts from your own neck of the woods. Private collections when possible, any public collections, guide books, etc. But the Robbins has the largest collection that is available for public viewing.
And I agree, the piece of quartz is just a natural pebble.
a good rule of thumb for an artifact is what was it used for?... in most cases the answer is obvious and when it is not, it is usually ALSO obvious (oddly enough) that the piece is an artifact.
Fred, please check out this link and if you look at the top of the page you will see one by monsterack on Stone Tools as well. Both of these posts show great examples of actual Stone Tools and their manufacture. If you do a search I'm sure there are several other as well.