It looks awfully dark for any Jasper, but the evidence seems to point to it being so. Kuntz also used bone, horn, mother of pearl, ivory, ebony, and glass for inlays. The cheek inlay on the Kuntz rifle in the Metropolitan Museum is glass or clear agate with some kind of exotic wood veneer or stone underneath - on close up examination neither Tom nor I could figure out what it was. For scale, the oval is about 3/4" long. Any guesses?
-Eric
Photo taken by Tom Curran, Permission to share publicly granted courtesy of the Metropolitan Museum in NYC.