Authigenic feldspar in a carbonate rock. The detrital feldspar is the bright blue grain in the center and the authigenic feldspar is the non-luminescing black region surrounding it.
This is one of the very first examples showing the usefulness of CL in studying authigenic feldspars and distinguishing them from their detrital counterparts.
This photo was originally taken by Dr. Miriam Kastner when she worked with Dr. Siever at Harvard in 1972. Dr. Kastner is now a Distinguished Professor of Earth Sciences at Scripps Institute of Oceanography. Recently, she was awarded the prestigious Francis P. Shepard Medal. By SEPM.