Crystal structure of sibirskite (CaHBO_3) by Monte Carlo simulation and Rietveld refinement

摘要

The crystal structure of sibirskite (CaHBO_3) was solved by the Monte Carlo simulation using powder X-ray diffraction data and confirmed by the Rietveld refinement. The mineral sibirskite is monoclinic with space group P2_1/a and cell constants of a = 8.643(6), b = 9.523(2), c = 3.567(3) A, and β = 119.23(3)°. The unit cell consists of independent atoms such as calcium, boron, hydrogen, and three oxygen atoms. The calcium atom is surrounded by six oxygen atoms in an octahedral coordination, and a symmetrical pair of edge-shared CaO_6, octa-hedra forming a double chain elongates the crystallographic c axis. The CaO_6, double chains are not directly connected to each other. The BO_3 triangles are linked to one vertical and two shared oxygen atoms in three CaO_6 double chains to form the sibirskite structure. Sibirskite is isostructural with nahcolite (NaHCO_3), which consists of NaO_6 double chains and CO_3 triangles.