Soliman , N. F. , Investigation of an Egyptian Alabaster Ore by Measuring its Natural Radioactivity and by NAA Using K0 Standardization and Comparator Method , Journal of Nuclear and Radiation Physics, Vol. 1, No. 1, 2006, p. 31 . ( 3 ) Sidraba I, Normandin KC, Cultrone G, Scheffler MJ , Climatological and regional weathering of Roman travertine. In: Prikryl R, Siegel P (eds) Architectural and sculptural stone in cultural landscape. Carolinum Press, Prague, 2004,pp 211–228 ; Sidraba I , Weatherability of Roman travertine. Ph.D. thesis Faculty of Material Science and Applied Chemistry, Institute of Silicate Materials, Riga Technical University, Latvia 2006 ,(unpublished) ; To¨ro¨k A , Black crusts on travertine: factors controlling development and stability. Env Geol, 2008 , 56:583–584. ( 4 ) the normally very low temperature of precipitation and extremely porous nature of travertine leads to a totally different appearance, it is not translucent and was never used in ancient Egypt , see: Klemm , D . and Klemm , R . , The building stones of ancient Egypt - a gift of its geology , African Earth Sciences 33 , 2001,p. 641. ( 5 ) Klemm , D . and Klemm , R . , op. cit. , 2001,p. 641