Fig. 9. This photomicrograph is from a deformed biotite-orthopyroxene gabbro layer (30-50 m wide and 20 km long) near Split Rock Pond northeast of Dover, New Jersey (USA). The gabbro gradationally becomes a sillimanite-garnet-muscovite-biotite gneiss along strike where planar deformation of the former gabbro is greatest. Reddish titaniferous biotite occurs in the photo. Plagioclase composition in the gabbro is An₈₀, but in the sillimanite gneiss is An₄₀. Maximum sizes of quartz vermicules in myrmekite shown in this transition rock are thick where K-feldspar is absent and less thick in the sillimanite gneiss where K-feldspar is present, but still quite thick.