Pavlovskyite Ca8(SiO4)2(Si3O10): A new mineral of altered silicate-carbonate xenoliths from the two Russian type localities, Birkhin massif, Baikal Lake area and Upper Chegem caldera, North Caucasus

Abstract

The new mineral pavlovskyite Ca 8 (SiO 4 ) 2 (Si 3 O 10 ) forms rims together with dellaite Ca 6 (Si 2 O 7 )(SiO 4 ) (OH) 2 around galuskinite Ca 7 (SiO 4 ) 3 CO 3 veins cutting calcio-olivine skarns in the Birkhin gabbro massif. In addition, skeletal pavlovskyite occurs in cuspidine zones of altered carbonate xenoliths in the ignimbrites of the Upper Chegem caldera (North Caucasus). The synthetic analog of pavlovskyite has been synthesized before and is known from cement-like materials. Isotypic to pavlovskyite is the synthetic germanate analog Ca 8 (GeO 4 ) 2 (Ge 3 O 10 ). The crystal structure of pavlovskyite, space group Pbcn, a = 5.0851(1), b = 11.4165(3), c = 28.6408(8) Å, V = 1662.71(7) Å 3 , Z = 4, has been refined from X-ray single-crystal data to R1 = 3.87%. The new colorless mineral has a Mohs hardness of 6-6.5, biaxial (-), α = 1.656(2), β = 1.658(2), γ = 1.660(2) (589 nm), 2V (meas) = 80(5)°, 2V (calc) = 89.9°, medium dispersion: r > v, optical orientation: X = b, Y = c, Z = a.For comparison with pavlovskyite, the crystal structure of kilchoanite Ca 6 (SiO 4 )(Si 3 O 10 ) from the Birkhin massif [space group I2cm, a = 11.4525(2), b = 5.0867(1), c = 21.996(3) Å, V = 1281.40(4) Å 3 , Z = 4] has been refined from single-crystal X-ray data to R1 = 2.00%.Pavlovskyite represents a 1:1 member of a polysomatic series with calcio-olivine γ-Ca 2 SiO 4 and kilchoanite Ca 6 (SiO 4 )(Si 3 O 10 ) as end-member modules. The structure is characterized by strongly folded trisilicate units (Si 3 O 10 ) interwoven with a framework of CaO 6 and CaO 8 polyhedra. Olivine-like slices with orthosilicate groups are interstratified with the characteristic trisilicate module of Ca 4 (Si 3 O 10 ) composition. Although the optical properties of pavlovskyite and kilchoanite are similar, both minerals can be distinguished by chemical analyses (different Ca/Si ratio), X-ray diffraction, and Raman spectroscopy. The new mineral is named after V.E. Pavlovsky , an outstanding geologist in the area of Eastern Siberia, in particular of the Baikal region.

Flux Synthesis and Structural and Spectroscopic Characterization of a Cobalt Europium Trisilicate

“…The Si–Si–Si angle in the recently reported compound K 2 Ca 3 Si 3 O 10 2 has a value of 97.54° and is close to those observed in other silicates, namely, BaREE 2 (Si 3 O 10 ) (REE = Y, Yb, Sc, Er, Gd) 41,1. A similar Si–Si–Si horseshoe arrangement with an angle of 98.38° was also reported by Galuskin et al in pavlovskyite 8…”

“…For further examples the reader is referred to ref 1. One more new compound in this group is the new mineral pavlovskyite Ca 8 (SiO 4 ) 2 (Si 3 O 10 ), which contains both SiO 4 and Si 3 O 10 groups in a 2:1 ratio 8…”

A Modular Concept of Crystal Structure Applied to the Thermal Transformation of α‐C2SH

“…An answer could be given by investigating the dehydration of bultfonteinite, Ca 4 [H 2 SiO 4 ][SiO 4 ](OH,F) 2 ·2H 2 O, where similar behavior to that of afwillite can be assumed. The higher C/S ratio of bultfonteinite might result in the formation of γ‐C 2 S and kilchoanite or even of the calcium‐rich Ca 8 [Si 3 O 10 ][SiO 4 ] 2 (recently found as mineral pavlovskiite) upon its dehydration.…”

Sharyginite, Ca3TiFe2O8, A New Mineral from the Bellerberg Volcano, Germany

“…Mostly, they are characterized by the presence of wadalite inclusions (Figure 5b). rusinovite, Ca10(Si2O7)3Cl2 [22], pavlovskyite, Ca8(SiO4)2(Si3O10) [23], edgrewite, Ca9(SiO4)4F2 [24], dzhuluite, Ca3SbSnFe 3+ 3O12 [25], etc. More geological information concerning this locality can be found in Gazeev et al [18], Galuskin et al [8,20] and Galuskina et al [26].…”