The crystal structure of the 11Å natural tobermorite Ca2.25[Si3O7.5(OH)1.5] · 1H2O

Abstract The crystal structure of a natural tobermorite from Zeilberg, Maroldsweisach, Germany (average formula Ca 2.2 5 [Si 3 O 7.5 s(OH) 1.5 ].-1H 2 O), is solved using the data obtained from an automatic diffractometer. For the structure determination only the sharp main reflexions are considered. The crystal data of the chosen subcell are: a′ = 5.586(4)Å, b′ = 3.696(2)Å, c = 22.779(7)Å, S.G Imm 2, V = 470.25Å 3 , Dx = 2.39 g/cm 3 , Dcxp = 2.43 g/cm 3 , and Z = 2. The disordered superposed structure is refined to a weighted R-value of 0.085. From the average structure the superposed chains are resolved and the tobermorite structure is then developed. One of the possible ordered tobermorite structures is monoclinic, space group P2l, with the unit cell dimensions: a m = 6.69 Å, b m = 7.39 Å, c m = 22.779Å, and y = 123.49°. The tobermorite has infinite Si 3 (O/OH) 9 chains running parallel b. The calcium atoms are coordinated by seven oxygen atoms.