The crystal structure of hollandite.

Abstract

The crystal structure of hollandite from Gowari Wadhona, India has been refined. Chemical formula determined by EPMA and moisture counter is (BaO.7sKO.38h.13 (Mn7.8sFeO.lS)8016'0.41H20. The structure is monoclinic, I2/m, and cell constants are a= 10.006(3)A, b=2 .866(1)A, c=9.7 46(2)A, {3=91.17(3)0. Each atom exists on a mirror plane (y=O, or 0.50). Manganese atom is in octahedral coordination. Mn06 octa-hedra are distorted and manganese atoms shift to unshared oxygens. The tunnel site is occupied by Ba2+, K+ and H20. These cations and moleculcs do not show continuous distribution along the tunnel but only one single peak is observed. This mineraI gives an X-ray powder pattern different from that of tetragonal hollandite. The relationship be-tween the site occupancies of tunnel cations and the powder diffraction intensities is discussed. As the occupancy of tunnel site increase, the intensity ratio of 1(200)+1(002) to 1(301)+I(Ï03) decreases.