Mineralogical Journal
Online ISSN : 1881-4174
Print ISSN : 0544-2540
ISSN-L : 0544-2540
THE CRYSTAL STRUCTURE OF BORAX
NOBUO MORIMOTO
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1956 Volume 2 Issue 1 Pages 1-18

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Abstract

The crystal structure of borax, Na2B4O7•10H2O, has been worked out by means of the sign relationships of structure factors and by the triple Fourier series method. The unit cell has the dimensions of a0=11.858Å, b0=10.674Å, c0=12.197Å and β=106°41′, and the space group is C62h. There are four chemical units of composition, Na2B4O7•10H2O in the unit cell. The coordinates of atoms were refined first by double Fourier series and the final triple Fourier series were carried out with 1763 terms. The standard deviations of coordinates finally obtained are 0.004Å for sodium atoms, 0.02Å for boron atoms and 0.02Å for oxygen atoms. Hydrogen atoms have been located from the consideration on the electrostatic valencies directed to the oxygen atoms and the interatomic distances between oxygen atoms.
The structure of borax is composed of chains of regular octahedra formed by water molecules around Na, running parallel to the c-axis. These chains build up a sheet holding isolated groups of B4O5(OH)4 in between them through hydrogen bonds. These sheets are parallel to (100) and held together mainly by hydrogen bonds. The structure formula of borax may best be represented with the expression B4O5(OH)4•Na28H2O.

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