Gibbsite, boehmite and haematite. Gove, Northern Territories, Australia
A pisolitic bauxite in which an angular fragment of an earlier pisolith has been extensively haematitized (blue-white, centre). Haematite is the only mineral that can be identified by reflected light microscopy in this section. The matrix, which is light red-brown due to finely disseminated iron minerals, comprises gibbsite and boehmite which were identified by X-ray diffraction.
Polished block, plane polarized light, x 40, air