Physics and Chemistry of Minerals

, Volume 45, Issue 5, pp 463–473 | Cite as

High-temperature crystal chemistry of layered calcium borosilicates: CaBSiO4(OH) (datolite), Ca4B5Si3O15(OH)5 (‘bakerite’) and Ca2B2SiO7 (synthetic analogue of okayamalite)

  • Maria G. Krzhizhanovskaya
  • L. A. Gorelova
  • R. S. Bubnova
  • I. V. Pekov
  • S. V. Krivovichev
Original Paper


The high-temperature behaviour of three Ca borosilicates has been studied by in situ powder high-temperature X-ray diffraction (HTXRD), differential scanning calorimetry and thermogravimetry in the temperature range 30–900 °C for natural samples of datolite, CaBSiO4(OH), and ‘bakerite’, Ca4B5Si3O15(OH)5, and a synthetic analogue of okayamalite, Ca2B2SiO7. The latter was obtained by heating datolite at 800 °C for 5 h. Datolite and bakerite start to dehydroxylate above 700 and 500 °C, respectively, and decompose fully to form a high-temperature modification of okayamalite, HT-Ca2B2SiO7, and wollastonite, CaSiO3 at about 730 °С. Above 900 °C, HT-okayamalite decomposes with the formation of wollastonite, CaSiO3, and metaborate CaB2O4. The latter melts at about 990 °C. Above 1000 °C, only the existence of wollastonite, CaSiO3 and cristobalite, SiO2 was observed. According to the HTXRD data, in the temperature range 30–500 °C, datolite and ‘bakerite’ demonstrate very similar and relatively low volumetric thermal expansion: α v  = 29 and 27 × 10−6 °C−1, respectively. A high thermal expansion anisotropy (α max/α min ~ 3) is caused by both the layered character of the crystal structures and the shear deformations of their monoclinic unit cells. The direction of maximum expansion is intermediate between the normal direction to the layers and the (a + c) vector. A possible transformation mechanism from the datolite to the okayamalite structure topology is proposed from geometrical considerations. The synthetic analogue of okayamalite, Ca2B2SiO7, undergoes a reversible polymorphic transition at about 550 °C with a decrease in symmetry from tetragonal to orthorhombic. The crystal structure of the high-temperature (HT) modification of okayamalite was solved from the powder-diffraction data [900 °C: P21212, a = 7.3361(4), b = 7.1987(4), c = 4.8619(4) Å, V = 256.76(3) Å3, R wp = 6.61, R Bragg = 2.68%].


Calcium borosilicate Datolite Bakerite Okayamalite Phase transition Thermal expansion Crystal structure High-temperature X-ray diffraction 



This research was financially supported by the Russian Foundation for Basic Research (no. 17-03-00887) and the President of Russian Federation grant for leading scientific schools (to SVK; Grant NSh-10005.2016.5). We are grateful to O.G. Bubnova and T. L. Panikorovsky for performing the thermal analysis, V. V. Shilovskih for performing the chemical analysis and S. N. Volkov for substantial help with the JANA2006 software. The XRD, TG and DSC studies have been carried out at the X-ray Diffraction Center and the chemical analysis has been performed at the Geomodel Center of St. Petersburg State University.

Supplementary material

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Supplementary material 1 (DOCX 14 KB)
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Supplementary material 2 (CIF 1 KB)


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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2017

Authors and Affiliations

  1. 1.Department of Crystallography, Institute of Earth SciencesSaint-Petersburg State UniversitySt. PetersburgRussia
  2. 2.Institute of Silicate ChemistryRussian Academy of SciencesSt. PetersburgRussia
  3. 3.Faculty of GeologyMoscow State UniversityMoscowRussia
  4. 4.Kola Science CentreMurmanskRussia

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