These are two views (obverse and reverse) of the same artifact. It would have been about 0.95 inches (24 mm) in diameter and it represents only one quarter of a coin. It was common practice to cut precious metal coins into halves, quarters, and eighths (bits) to make change at times when specie (coinage) was in short supply. In North America, that condition continued relatively unabated until the middle of the 19th century. Base metal coins (copper alloys, typically) did not have the full faith of Britain's subjects or of early American nationals. Gold and silver coins, regardless of face value or changing exchange rates, were always gold and silver and, therefore, worth something.
Chances are that this is either a Spanish coin, minted in the New World, or an English or Scottish coin. It likely dates to the 17th or 18th century. Pete found the image below of a King George III (Great Britain) 1787 shilling, but it is only one example of many types of coins and only a numismatist can narrow down the range of possibilities.
Such finds often catch the attention of excavators and visitors. This one was overlooked and merely pulled from the screen and washed without being recognized. While it comes from the plowzone overlying the earthfast building and cellar partially exposed by Pete and his crew, it isn't terribly informative because we can't relate it directly to those 18th-century features. Moreover, coins often are difficult to interpret archaeologically because they remain in circulation well after their mint dates. A 1680s coin of precious metal, say an English shilling or a Spanish two-reale, could still make the rounds of world markets in the late 18th or early 19th century. The fact that both faces of the coin that we recovered have been nearly worn away suggests that it remained in circulation for many years before its last possessor lost it.
Oh, yeah; if you are wondering about the coin's current value...I don't know and it is unethical for archaeologists to value archaeological finds. It is okay, however, for us to bet, and I bet this thing is worth as much as the silver of which it is made, calculated in terms of weight and purity. In other words, probably not very much.