Plate 11

(a) — Biotite crystal from Murray Bay, Canada; (b) — Po halo containing specimens of granite from New Hampshire, the dark areas are biotite crystals; (c) — Zircon crystals extracted from granite drill cores taken from a depth of about 15,000 ft.; (d) — Rhyolite from 1,683.3 ft. (specimen obtained from J. Eichelberger, Sandia National Labs)