1. Boyadjiev, S. 1971. Petrology of the Plana pluton. Bulletin of the Geol. Institute, series Geochem., Mineral., Petrogr., 20, 219-242 (in Bulgarian with English abstract).
2. Dabovski, Ch. 1975. Structural studies in Plana pluton. Geotect., Tectonophys., Geodyn., 2, 53-63 (in Bulgarian).
3. Dobrev, N.D., Y. Sasaki, Y. Wakizaka. 2002. Granite outcrop classification by the state of weathering: A case study of Iwaki City. Proc. of the Japan Society of Engineering Geology Meeting, Takamatsu, 31.10-01.11.2002, 339-342.
4. Iliev, I., N. Katskov. 1990. Geological map of Bulgaria on Scale 1: 100 000. Ihtiman Map Sheet. Geology and Mineral Resources Committee, Enterprise of Geophysical Survey and Geological Mapping.
5. Iliev-Broutchev, I., ed. 1994. Geological hazards in Bulgaria – map in scale 1:500 000 and explanatory text. Military Topographic Service, Troyan/Publishing House of Bulgarian Academy of Sciences, Sofia, 143 p. (in Bulgarian with English abstract).