Gibbsite, boehmite and haematite. Gove, Northern Territories, Australia

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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

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