Abstract: A polymeric silicate material having a substantially fibre- or flake-like microstructure is manufactured from a starting material comprising mainly natural or synthetic silicate mineral e.g., Olivine and/or Granate (garnet), having a hardness exceeding the value 6 on the Moh's hardness scale and which are compound(s) having the general formulae:2(R.sup.I O).multidot.SiO.sub.2wherein R.sup.I may be the same or different and is Mg and/or Fe; and3(R.sup.II O).multidot.R.sub.2.sup.III O.sub.3 .multidot.3 SiO.sub.2wherein R.sup.II may be the same or different and is Mg, Fe and/or Ca; and R.sup.III is Al or Fe, by finely dividing said material to a specific surface area of at least 15,000 cm.sup.2 /cm.sup.3, measured according to Blaine, and subsequently hydrothermally treating the resultant powderous starting material at a temperature of approximately 175.degree.-325.degree. C. and a pH of at least 9 in the presence of water or condensed steam.