Fig. 17. Note that microcline (grid-twinning; black; upper left, center) penetrates along an irregular fracture to the core of a speckled, albite-twinned plagioclase crystal (top center and right side). Another plagioclase grain (bottom center) has irregular projections (left end of crystal) which stick out into the adjacent microcline (bottom left). The diagonal truncation by the microcline of the albite-twin lamellae and zoning (altered albitic edge) of this same plagioclase crystal along the bottom right side suggests that a portion of this plagioclase grain has been replaced by the microcline.