TY - JOUR
T1 - Clinotobermorite, Ca5[Si3O8(OH)]2 · 4 H2O - Ca5[Si6O17] · 5H2O, a natural C-S-H(I) type cement mineral
T2 - Determination of the substructure
AU - Hoffmann, C.
AU - Armbruster, T.
PY - 1997
Y1 - 1997
N2 - The substructure of natural clinotobermorite Ca5[Si3O8(OH)]2 · 4 H2O - Ca5[Si6O17] · 5H2O from the Wessels mine, Kalahari manganese field, South Africa, was determined from single-crystal X-ray data. The diffraction pattern (monoclinic: a =11.19 Å, b = 7.29 Å, c = 22.46 Å, β = 96.97°) is characterised by rather diffuse reflections of the type hkl with h, k = 2n + 1. The substructure (space group I2/m, Z = 1, a/2 = 5.593(6) Å, b/2 = 3.645(4) Å, c = 22.46(3) Å, /3 = 96.97(2)°) was solved from the sharp Bragg reflections (hkl, with h, k = 2n) and refined on the basis of 1877 unique reflections to R(F) = 6.7%. The structure of clinotobermorite is closely related to the one of so called 11 A tobermorite Ca5Si6O16(OH)2·2H2O (pseudo-orthorhombic, a =11.17 Å, b = 7.38 Å, c = 22.6 Å). In both minerals layers parallel (001), formed by seven-fold co-ordinated Ca, are flanked on either side by wollastonite-like [Si3O9] single chains (ca. 7.3 Å periodicity along b) creating a sandwich-like assemblage. The short b/2 axis (3.645 Å) and the short a/2 axis (5.593 Å) of the subcell are caused by an overlay of two half-occupied single chains of tetrahedra with one shifted by b/2 against the other. In clinotobermorite the sandwich-like layers are stacked along c yielding an interlayer distance of 4.5 A with a free aperture of 3.2 A where additional Ca ions and H20 molecules connect the sandwich units. Clinotobermorite with 4-5 H20 represents a much denser structure than 11 A tobermorite with only 2 H2O or 14 A tobermorite with ca. 6 H2O (pseudo-orthorhombic, a =11.17 Å, 6 = 7.38 Å, c = 27.94 Å). The substructure of clinotobermorite can be interpreted as either composed of ‘Dreiereinfachketten’ leading to the formula Ca5[Si3O8(OH)]2 -4H2O, or of ‘Dreierdoppelketten’ leading to the formula Ca5[Si6O17] · 5 H2O, or of a mixture of both variants. The surface structure of clinotobermorite was studied by atomic force microscopy (AFM) where low magnifications reveal a complex layering or twinning parallel (001). * Correspondence author (e-mail: [email protected]) High resolutions scans parallel (100) establish enhanced contrast fringes with a periodicity of ca. 10 A interpreted as the repeat distance of the Ca polyhedral layers parallel to c.
AB - The substructure of natural clinotobermorite Ca5[Si3O8(OH)]2 · 4 H2O - Ca5[Si6O17] · 5H2O from the Wessels mine, Kalahari manganese field, South Africa, was determined from single-crystal X-ray data. The diffraction pattern (monoclinic: a =11.19 Å, b = 7.29 Å, c = 22.46 Å, β = 96.97°) is characterised by rather diffuse reflections of the type hkl with h, k = 2n + 1. The substructure (space group I2/m, Z = 1, a/2 = 5.593(6) Å, b/2 = 3.645(4) Å, c = 22.46(3) Å, /3 = 96.97(2)°) was solved from the sharp Bragg reflections (hkl, with h, k = 2n) and refined on the basis of 1877 unique reflections to R(F) = 6.7%. The structure of clinotobermorite is closely related to the one of so called 11 A tobermorite Ca5Si6O16(OH)2·2H2O (pseudo-orthorhombic, a =11.17 Å, b = 7.38 Å, c = 22.6 Å). In both minerals layers parallel (001), formed by seven-fold co-ordinated Ca, are flanked on either side by wollastonite-like [Si3O9] single chains (ca. 7.3 Å periodicity along b) creating a sandwich-like assemblage. The short b/2 axis (3.645 Å) and the short a/2 axis (5.593 Å) of the subcell are caused by an overlay of two half-occupied single chains of tetrahedra with one shifted by b/2 against the other. In clinotobermorite the sandwich-like layers are stacked along c yielding an interlayer distance of 4.5 A with a free aperture of 3.2 A where additional Ca ions and H20 molecules connect the sandwich units. Clinotobermorite with 4-5 H20 represents a much denser structure than 11 A tobermorite with only 2 H2O or 14 A tobermorite with ca. 6 H2O (pseudo-orthorhombic, a =11.17 Å, 6 = 7.38 Å, c = 27.94 Å). The substructure of clinotobermorite can be interpreted as either composed of ‘Dreiereinfachketten’ leading to the formula Ca5[Si3O8(OH)]2 -4H2O, or of ‘Dreierdoppelketten’ leading to the formula Ca5[Si6O17] · 5 H2O, or of a mixture of both variants. The surface structure of clinotobermorite was studied by atomic force microscopy (AFM) where low magnifications reveal a complex layering or twinning parallel (001). * Correspondence author (e-mail: [email protected]) High resolutions scans parallel (100) establish enhanced contrast fringes with a periodicity of ca. 10 A interpreted as the repeat distance of the Ca polyhedral layers parallel to c.
UR - http://www.scopus.com/inward/record.url?scp=0002950060&partnerID=8YFLogxK
U2 - 10.1524/zkri.1997.212.12.864
DO - 10.1524/zkri.1997.212.12.864
M3 - Article
AN - SCOPUS:0002950060
SN - 1433-7266
VL - 212
SP - 864
EP - 873
JO - Zeitschrift fur Kristallographie - New Crystal Structures
JF - Zeitschrift fur Kristallographie - New Crystal Structures
IS - 12
ER -
