Biotite is black mica. Another rock found here is the gray-brown Julian schist, a metamorphic with twisted, streaked bands of darker and lighter material that originated as seafloor sediment ...

Within the schist occurred sediments with alteration and mineralization at 124.7-153.2m and 186.5-198m, in additional a complex zone from 216-240.8m included talc schist, biotite schist and the ...