Gillespite has been studied by means of rotation, oscillation, Laue and powder x-ray patterns. It belongs to the space group D84h—P/ncc. The unit cell, a = 7.495±0.010 Å, c = 16.050 ±0.010 Å, contains 4 BaFeSi4O10.
A structure with eleven parameters has been found which yields satisfactory agreement of calculated and observed intensities. It is a silicate sheet structure with oxygen atoms in three kinds of positions and unshared corners of SiO4 tetrahedra on both sides of the sheets. Single and double fourier summations give an excellent check on the structure. Interatomic distances are of expected magnitude. Barium has an 8-fold coordination and iron a 4-fold coordination.
The leaching of gillespite is discussed.