Mel, your piece is the exact size and shape of a perforated whetstone illustrated in Curtis Hoffman's "A Handbook of Indian Artifacts from Southern New England"(1991, Ma. Archaeological Society, p. 71). When these whetstones are perforated, they are countersunk pecked from both sides, followed by drilling. The materials most often used are argillite(slate), schist, and sandstone. So your piece may be a perforated whetstone, which are usually in the 6-8" length range. If used as a whetstone, it would show "wear from long even lengthwise strokes of rubbing. Because of this, and the narrow proportions of this honing stone, it is thought to have been used in grinding the blades of gouges and other woodcutting implements"(Hoffman, p. 71) I cannot rule out very large pendant, but the size, shape, and countersunk perforation suggests a whetstone.