The crystal structure of hurlbutite, CaBe2P2O8 (a = 8.299Å; b = 8.782 Å; c = 7.798 Å; β = 90.5°; space group P21/a) has been refined to an R factor of 0.062. The refinement converged only when the signs of the z-coordinates reported by Bakakin and Belov (1959) were interchanged.

Hurlbutite is a framework of alternating BeO4 and PO4 tetrahedra with Ca in an irregular coordination polyhedron, which may be considered either 7- or 9-coordinated: (cavii - o) = 2.469 Å, (Caix -O) = 2.620 Å. The mean Be-O distances are 1.620 and 1.629 Å, and the mean P-O distances are 1.527 and 1.533 Å.

The trends observed between T-O bond lengths, oxygen coordination number, and Mulliken bond overlap populations for Be-O→P and P-O→Be bonds in hurlbutite are similar to those in anorthite and danburite. It is also demonstrated that the overlap populations account for part of the extrinsic effects of the Ca atoms, even thoueh Ca was not included in the extended HÜckel molecular orbital calculations.

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