Blue corundum, tourmaline, topaz, mica and other minerals, part of the Deleff Collection in the Museum of Mineralogy, Petrography and Mineral Resources, “St. Ivan Rilski” University of Mining and Geology, Sofia (photo by R. I. Kostov).

Giant quartz unque minerals

Blue corundum, tourmaline, topaz, mica and other minerals, part of the Deleff Collection in the Museum of Mineralogy, Petrography and Mineral Resources, “St. Ivan Rilski” University of Mining and Geology, Sofia (photo by R. I. Kostov).