Abstraft
As a part of a detailed study of the structures and crystal chemistry of the aluminum silicate minerals the crystal structure of andalusite, Al2SiO5, has been refined. Twelve cycles of least-squares refinement on the IBM 704 computer reduced the disagreement factor, R, for 354 hkl reflections from an initial value of 43.9% to a final value of 5.7%.
The original structure determined by Taylor1 was found to be fundamentally correct. Chains of aluminum octahedra sharing edges lie parallel to the c axis. These octahedra depart appreciably from regularity; two of the Al-O bond distances are 1.83 Å, two are 1,89 Å, and the two Al-O distances normal to the c axis are 2.09 Å. The octahedral chains are linked together by a framework of silicon tetrahedra and five-coordinated aluminum groups. The Si-O bond distances are 1.64 Å, 1.62 Å, 1.63 Å, and 1.63 Å. The Al-O bond distances in the five-coordinated group are 1.82 Å, 1.82 Å, 1.82 Å, 1.84 Å and 1.88 Å. The five-coordinated groups occur in pairs sharing an edge whose length is 2.25 Å.
