• journal_title：The Canadian Mineralogist
• Contributor：Wei Sun ; Ya-Xi Huang ; Zucheng Li ; Yuanming Pan ; Jin-Xiao Mi
• Publisher：Mineralogical Association of Canada
• Date：2011-
• Format：text/html
• Language：en
• Identifier：10.3749/canmin.49.3.823
• journal_abbrev：Can Mineral
• issn：0008-4476
• volume：49
• issue：3
• firstpage：823
• section：Articles

Sibirskite, parasibirskite and priceite, synthesized in aqueous solutions at temperatures from 80 to 240°C, have been investigated by single-crystal X-ray refinements of the structure. Sibirskite and parasibirskite are dimorphs of CaHBO₃. Sibirskite at 295 K crystallizes in space group P12₁/c1 (no. 14), with a 3.5624(7), b 9.5225(19), c 8.6231(17) Å, β 119.452(3)°, V 254.72(9) ų, and Z = 4. Parasibirskite at 295 K crystallizes in space group P12₁/m1 (no. 11), with a 6.6994(13), b 5.4269(11), c 3.5534(7) Å, β 93.048(11)°, V 129.01(5) ų, and Z = 2. Priceite, (Ca₂(H₂O)[B₅O₇(OH)₅]), at 173 K crystallizes in space group of P12₁/ c1 (no. 14), with a 11.580(3), b 6.9844(19), c 12.352(3) Å, β 110.573(9)°, V 935.3(4) ų, and Z = 4. Our refinements allow determination of the positions of boron and hydrogen atoms in these minerals, which was not possible in previous powder XRD studies. In particular, the isolated [BO₂(OH)] groups in sibirskite and parasibirskite are characterized by a long B–OH bond and two short B–O bonds, different from the [BO₃] and [B(OH₃)] groups in nesoborates. Periodic density functional theory (DFT) calculations for sibirskite and parasibirskite support those results of structure refinements and suggest that parasibirskite undergoes a displacive phase-transition involving hydrogen ordering below 173 K. Sibirskite and parasibirskite left in their parental solutions at ambient conditions decompose to form calcite.