The pegmatite crops out as a nearly circular knob about 300 feet in diameter. Surrounded by quartz-mica schist. The dip is steep to the northeast. Lbite-quartz-perthite pegmatite. A few coarse-grained quartz-perthite.Bulk composition and variations in composition within a structurally simple pegmatite in the southern Black Hills, South Dakota, have been determined from analyses of a set of drill core samples collected from the hanging wall to the footwall. Reliable data of this kind are uncommon, for pegmatite have textures and structures that put many difficulties in the way of one who tries to collect representative samples; yet such data are indispensable to a proper understanding of the petro genesis of pegmatite.