The crystal structure of the 11 A natural tobermorite Ca 2 . 2 s [
نویسنده
چکیده
The crystal structure of a natural tobermorite from Zeilberg, Maroldsweisach, Germany (average formula Ca2.2s[Si307.s(OH)1.5]'1 H20), 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) A, b' = 1696(2) A, C = 22.779(7) A, S.G. Imm2, V = 470.25 A3, Dx = 2.39 g/cm3,Dexp.= 2.43 gjcm3, 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, spacegroup P2b with the unit cell dimensions: am = 6.69 A, bm = 7.39 A, Cm = 22.779 A, and'}' = 123.49°. The tobermorite has infinite Si3(OjOH)g chains running parallel b. The calcium atoms are coordinated by seven oxygen atoms.
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