Xenolith??  I never heard this term before Friday's Tar Heel Club trip to Wake Stone Corp.'s Knightdale quarry.  So we learned from the quarry staff that it's an inclusion of an older rock by the flow or eruption of a younger igneous rock.  There were a couple of large xenoliths in the quarry walls.  The photo shows a massive area of dark gneiss, a more ancient rock, encased by a light-colored and more recent granite flow.

No amethyst was found on the trip, and apparently it's rare as hen's teeth. The only collectible mineral I saw was molybdenite, and almost all of that came from one large block that was broken into smaller take-home pieces.