Abstract

From Iberville Parish, Louisiana. Space group P1, unit cell dimensions: a = 17.495(4), b = 6.487(1), c = 6.313(1) angstrom; alpha = 60.77(1), beta = 79.56(1), gamma = 83.96(1) degrees ; Z = 1. The R-factor is 0.020 for 4490 reflections. The structure of parahilgardite is a three-dimensional framework whose building blocks are three crystallographically distinct pentaborate polyanions [B 5 O 12 ] (super 9-) , each consisting of three (BO 4 ) tetrahedra and two (BO 3 ) triangles. These polyanions, two of which are in l and one in d configuration, form three distinct single chains by sharing tetrahedral corners along the c axis.--Modified journal abstract.

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