HEATING PRODUCTS OF GLAUCONITIC MATERIALS

Four practically pure, mutually chemically different, glauconitic mate rials, as mixtures of glauconite and interstratified glauconites-smect ites (having relatively small expandibility) were isolated from the Lo wer Miocene sandstones at several localities in Croatia. Glauconitic m aterials were successively heated for 3 hours at 980, 1080, 1180, and 1300 degrees C. The heat-treated samples were analysed by means of X-r ay powder diffraction (identification, determination of the unit-cell parameter a of magnesioferrite and semiquantitative phase analysis). T he amounts of FeO in samples were also determined. On the basis of the data obtained for the heat-treated samples and the data on the starti ng glauconitic materials (using the ''wet'' chemical analysis, infrare d spectroscopy, differential thermal analysis and thermogravimetry, be side X-ray diffraction), the following conclusion was drawn: (1) after the destruction of the crystal structure of glauconite, the heating p roducts at 980 degrees C were an amorphous fraction (glass) and magnes ioferrite; (2) in the materials for which the content of Fe3+ was much bigger than that of Al-VI magnesioferrites were formed which were sol id solutions of MgFe2O4, gamma-Fe2O3 and Fe3O4; otherwise, in the mate rial with a high amount of Al-VI a magnesioferrite was formed which al so contained Al; (3) the fraction of magnesioferrite gradually decreas ed as the temperature of heating increased to 1080 and 1180 OC, while hematite and enstatite were formed; (4) after heating at 1300 degrees C magnesioferrite was again the single crystalline phase, but containi ng a bigger amount of divalent iron and having a bigger unit-cell para meter a than magnesioferrite formed at 980 degrees C.