Fig. 18. Photomicrograph of K-feldspar (gray and black, cross-hatch twinned) with remnants of plagioclase (tan) which extend through the K-feldspar in parallel optical continuity. Ground mass minerals consist of quartz (cream, gray, white), biotite (brown), hornblende (brown), and additional plagioclase (tan, gray). In hand specimen, this K-feldspar would appear as a tiny pink crystal in the midst of the black plagioclase amphibolite.