Abstract
The crystal structure of hollandite from Gowari Wadhona, India has been refined. Chemical formula determined by EPMA and moisture counter is (Ba0.75K0.38)1.13 (Mn7.85Fe0.15)8O16·0.41H2O. The structure is monoclinic, I2⁄m, and cell constants are a=10.006(3)Å, b=2.866(1)Å, c=9.746(2)Å, β=91.17(3)°. Each atom exists on a mirror plane.(y=0, or 0.50). Manganese atom is in octahedral coordination. MnO6 octahedra are distorted and manganese atoms shift to unshared oxygens. The tunnel site is occupied by Ba2+, K+ and H2O. These cations and molecules do not show continuous distribution along the tunnel but only one single peak is observed. This mineral gives an X-ray powder pattern different from that of tetragonal hollandite. The relationship between the site occupancies of tunnel cations and the powder diffraction intensities is discussed. As the occupancy of tunnel site increase, the intensity ratio of I(200)+I(002) to I(301)+I(-103) decreases.
