The invention relates to a method for preparing a composition, that is a talcose composition, comprising synthetic mineral particles which contain silicon, germanium and metal, have a crystalline and lamellar structure, and are of formula (SixGe1−x)4M3O10(OH)2, wherein M is at least one divalent metal and is of formula Mgy(1)COy(2)Zny(3)Cuy(4)Mny(5)Fey(6)Niy(7)Cry(8), and x is a real number of the interval [0; 1]. According to said method, a gel containing silicon, germanium and metal, of formula —(SixGe1−x)4M3O11, n′H2O—, in the liquid state, is subjected to a hydrothermal treatment over a defined period of time and at a temperature of between 300° C. and 600° C., said time and temperature being selected according to the desired particle size and structural stability for the mineral particles containing silicon, germanium and metal, to be prepared.