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)

Table 5. Chemical Composition of Bauxite 1 2 3 4 5 6 A1

2

0

3 71.9 44.6 42.4 34.2 34.4 25.6 Si0

2 1.6 16.5 23.7 39.6 23.9 27.5 Fe

2

Ő

3 10.0 19.4 14.3 7.9 11.5 27.4 Ti0

2 1.6 1.8 1.8 1.8 1.5 1.4 CaO — — 9.5 Ign. loss. 14.4 14.1 12.7 13.5 17.7 13.7 Rest 0.5 3.6 5.1 3.0 1.5 4.4 Analyst: Laboratory of Enterprise for Bauxite Research Balatonalmádi. Fig. 1. Differential thermal analysis curve^of kaolinite. It is considered to be the decomposition product of pyrite under highly oxidative conditions. According to our present knowledge corundum, present in small amounts, is an allothigenic mineral here. Iron minerals On the basis of earlier niineralogical investigations iron was thought to be present in the form of hematite and much less in goethite. It has now became clear that goethite is much more common than hitherto believed. Its presence is suggested also by the abundance of yellow bauxites. In these types the amount of goethite exceeds 20 percent; hematite is quite subordinate. In the red-coloured varieties hematite is the dominant iron mineral but with a small amount of goethite always recognizable. X-ray diffraction combined with heating experiments was used to determine the very small amount of goethite. In the case of more goethite the DTA method was used (Fig. 2.). Hematite occurs as an allothigenic constituent also in the heavy mineral fraction. Fig. 2. Differential thermal analysis curves of bauxite types. 1. red bauxite; 2. pisolitic bauxite; 3. bauxite containing calcite; 4. yellow bauxite.