Kaszab Zoltán (szerk.): A Magyar Természettudományi Múzeum évkönyve 63. (Budapest 1971)
Embey-Isztin, A.: Contribution to the mineralogy of the bauxites from Nézsa (North-Hungary)
from the peaks of other minerals (diaspore, goethite, anatase, etc.) the plusintensities due to the presence of kaolinite. To eliminate any preferred orientation of kaolinite, a number of diffraction patterns were made of the pure kaolinite material. Grain-size distribution of the bauxite The determination of the dominant grain size of the bauxite was made by a statistical evaluation of electron micrographs (Plate I. 1—2.). The mean size of the grains of Nézsa bauxites is 0.35 millimicron. For all Hungarian bauxites this value lies between 0.1 and 0.5 millimicron. The interference lines on the X-ray patterns of the Nézsa bauxites are narrower than those of the other Hungarian bauxites, particularly those of the gibbsitic types. It is probable therefore that the average grain size of the gibbsitic types approaches the lower limit of 0.1 millimicron and that of the diasporic ones the upper limit of 0.5 millimicron. Although most bauxites are of colloidal grain size this does not exclude the presence of small amounts of larger grains visible under the microscope. In effect, in certain thin sections diaspore crystals of 0.4 mm. size and kaolinite grains of 0.06 mm. size have been observed. Minerals of aluminium On the basis of earlier DEBYE — SCHERRER patterns we expected small amounts of gibbsite and boehmite in the Nézsa bauxites. The earlier data were not confirmed by our X-ray investigations. Considering the oxidative redox conditions of the deposit, the presence of boehmite is quite improbable also theoretically. Diaspore is the only allitic mineral of the Nézsa bauxite deposit. The diaspore content varies over a wide range: there are bauxitic clays of 1 percent diaspore content, and high-grade bauxites with a diaspore content of 80 percent. Most of the diaspore is finely dispersed, submicroscopic; microscopic diaspore is scarce. The few grains encountered invariably exhibit the cleavage after (010). Since the Nézsa bauxite deposit shows no recognizable traces of tectonic or thermal effects we can suppose that diaspore had formed during bauxitization as a diagenic constituent. One sample exhibited uncertain alunite lines. Little alunite patches were found in the Nézsa bauxites by J. Kiss. Table 4. X-Ray Diffraction Data for Nézsa Kaolinite Zr-Filtered Molybdenum Ka Radiation d(Â) I hkl 7.15 80 001 4.37 82 110 4.18 80 111 3.84 50 02Ï 3.57 100 002 3.38 37 111 3.16 18 112 2.77 7 022 2.55 55 130 20l 130 2.52 57 13Ï 112 2.49 15 13Ï 200 112 2.34 90 202 131 113 2.13 8 023 + 1.99 30 132 1.93 20 132 + 1.89 17 133 + 1.79 7 004 1.68 38 241 1.66 48 204+ 133+ 1.61 15 133+ 1.58 12 134+ 1.49 48 060 331 331
