Redetermination of katayamalite, KLi3Ca7Ti2(SiO3)12(OH)2

The crystal structure of katayamalite, ideally KLi3Ca7Ti2(SiO3)12(OH)2 (potassium trilithium heptacalcium dititanium dodecasilicate dihydroxide), was previously reported in triclinic symmetry (C-1), with isotropic displacement parameters for all atoms and without the H-atom position [Kato & Murakami (1985 ▶). Mineral. J. 12, 206–217]. The present study redetermines the katayamalite structure with monoclinic symmetry (space group C2/c) based on single-crystal X-ray diffraction data from a sample from the type locality, Iwagi Island, Ehime Prefecture, Japan, with anisotropic displacement parameters for all non-H atoms, and with the H atoms located by difference Fourier analysis. The structure of katayamalite contains a set of six-membered silicate rings interconnected by sheets of Ca atoms on one side and by an ordered mixture of Li, Ti and K atoms on the other side, forming layers which are stacked normal to (001). From the eight different metal sites, three are located on special positions, viz. one K and one Li atom on twofold rotation axes and one Ca atom on an inversion center. The Raman spectrum of kataymalite shows a band at 3678 cm−1, similar to that observed for hydroxyl-amphiboles, indicating no or very weak hydrogen bonding.

The crystal structure of katayamalite, ideally KLi 3 Ca 7 Ti 2 -(SiO 3 ) 12 (OH) 2 (potassium trilithium heptacalcium dititanium dodecasilicate dihydroxide), was previously reported in triclinic symmetry (C1), with isotropic displacement parameters for all atoms and without the H-atom position [Kato & Murakami (1985). Mineral. J. 12,[206][207][208][209][210][211][212][213][214][215][216][217]. The present study redetermines the katayamalite structure with monoclinic symmetry (space group C2/c) based on single-crystal X-ray diffraction data from a sample from the type locality, Iwagi Island, Ehime Prefecture, Japan, with anisotropic displacement parameters for all non-H atoms, and with the H atoms located by difference Fourier analysis. The structure of katayamalite contains a set of six-membered silicate rings interconnected by sheets of Ca atoms on one side and by an ordered mixture of Li, Ti and K atoms on the other side, forming layers which are stacked normal to (001). From the eight different metal sites, three are located on special positions, viz. one K and one Li atom on twofold rotation axes and one Ca atom on an inversion center. The Raman spectrum of kataymalite shows a band at 3678 cm À1 , similar to that observed for hydroxyl-amphiboles, indicating no or very weak hydrogen bonding.

Experimental
The katayamalite specimen used in this study is from the type locality, Iwagi Island, Inland Sea, Ehime Prefecture, Japan and is in the collection of the RRUFF project (deposition http://rruff.info/R120164). Its chemical composition was measured using a CAMECA SX100 electron microprobe (14 analysis points), yielding the empirical chemical formula, calculated on the basis of 38 anions, (K 0.89 Na 0.12 ) Σ1.01 Li 3.21 (Ca 6.87 Mn 0.04 Ba 0.02 ) Σ6.93 (Ti 1.79 Zr 0.14 Fe 0.04 Sn 0.02 ) Σ1.99 (SiO 3 ) 12 (OH 1.55 F 0.45 ). The Raman spectrum of katayamalite was collected from a randomly oriented crystal at 100% power on a Thermo Almega microRaman system, using a solid-state 532 nm laser, and a thermoelectrically cooled CCD detector. The laser is partially polarized with 4 cm -1 resolution and a spot size of 1 µm.

Refinement
For simplicity, the ideal chemical formula, KLi 3 Ca 7 Ti 2 (SiO 3 ) 12 (OH) 2 , was assumed during the refinement. The structure was refined in space group C2/c, using the coordinates proposed by Baur & Kassner (1992). The maximum residual electron density in the difference Fourier maps was located at ( (530) were omitted from the refinement due to large differences between calculated and measured intensities.

Figure 2
Six-membered silicate ring in tremolite (Yang & Evans, 1996). Pink, red, and blue represent SiO 4 groups, oxygen and hydrogen atoms, respectively.  Six-membered silicate rings in the packing of the structure of katayamalite. Pink represents SiO 4 groups.

Figure 4
The crystal structure of katayamalite with layers stacked normal to (001). The SiO 4 ring layers are connected by Ca atoms on one side and by Li, Ti and K atoms on other side. Pink, brown, green, orange and yellow represent SiO 4 groups, Ca, Li, Ti and K atoms, respectively. Displacements ellipsoids are drawn at the 99.999% probability level.  The Raman spectrum of katayamalite. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.