Abstract: Trabzonite, ideally Ca4Si3O10.2H2O, has been found near îkizdere at NW of Varda Yaylası(Rize) (near Trabzon country) - Turkey and occurs in skarn produced by granitic intrusion in volcanosedimentary formations. Associated minerals are : spurrite, rustumite, perovskite, calcite, vesuvianite,tobermorite, garnet, defernite, killalaite, hillebrandite and molybdenite. The crystals, colourless, are smallirregular or hypidiomorphs from 0.1 to 0.2 mm with a white streak and lustre vitreous; transparent.The hardness could not be measured because of small size. Chemical composition determined byelectron microprobe is: CaO 50.2, MgO 0.13, MnO 0,04, Na2O 0.3, A12O3 0.05, SiO2 4038 and H2O7(weight loss), Total 98,1 %. The crystal system is monoclinic, space group 1?21 or P21/m with a=6.895(2),b = 20,640 (3), c = 6,920 (2)A°, ß = 985 and Z = 4. The a : b : c ratio calculated from unit-cell parametersis 0.3341: 1: 0.3353. The strongest lines in the X-ray powder diffraction pattern (dAe for CuK y weak to moderate, Optical orientation : X A c c* 8°, y = b, Z = a.Trabzonite is named for to honour the vilâyet of Trabzon.