Fig. 15. The altered plagioclase grains (brown speckled; albite-twinned; left side) were likely part of a former larger plagioclase crystal before being broken into smaller blocks. This crystal would have extended into the area now occupied by microcline (black; right side). A relatively sharp boundary occurs on the photo from the top vertically downward between the plagioclase (left side) and the microcline (right side), black and gray). However, a portion of the speckled-brown plagioclase projects into the dark microcline as an irregular pointed remnant that sticks out from the vertical edge. This remnant suggests that K-replacement of adjacent plagioclase has occurred because such textures are not commonly seen where both feldspars crystallize from melt. In the lower left corner of the photo, the microcline (black) can be seen to penetrate (upward and to the left) into the altered plagioclase along an irregular fracture. In the microcline (right side), island remnants of plagioclase with albite-twin lamellae are aligned parallel with the twin lamellae of the speckled grains outside the microcline (left side), and still more aligned remnants are abundant beyond what is seen in the photograph.