New data on the nature of fine and ultrafine lamellae in titanomagnetite
Krasnova, Nataly I.; Krezer, Yuri L.
European Journal of Mineralogy Volume 7 Number 6 (1995), p. 1361 - 1372
published: Dec 27, 1995
manuscript accepted: Jun 27, 1995
manuscript received: Nov 10, 1994
ArtNo. ESP147050706009, Price: 29.00 €
Abstract Microtextural features and the chemical composition of intergrowths in titanomagnetite from various rocks have been investigated by scanning electron microscopy and energy-dispersive microanalysis on samples etched with concentrated HC1 to allow the analysis of ultrathin (about 1 μm) lattice intergrowths. All intergrowths in titanomagnetite fall into the following groups: 1) ilmenite-geikielite; 2) spinel-magnetite and magnesian magnetite; 3) spinel-pleonaste; 4) spinel-hercynite. Compositional data are presented here for the first time for most of these intergrowths. Their nature has been confirmed in two specimens by X-ray diffraction studies on lamellar phases isolated from the titanomagnetite by repeated treatment with HC1 and magnetic separation. These lamellar phases proved to be members of the ilmenite-geikielite group, in disagreement with the conventional opinion that they consist of ulvospinel. Until now ulvospinel has not been found in the lamellar intergrowth types in the studied titanomagnetites. Some spinel and ilmenite inclusions developed as skeletal or isometric crystals, simultaneously with the growing magnetite grains; most inclusions, however, formed as a result of titanomagnetite exsolution at decreasing temperatures. The correct identification of the lamellar and other phases in titanomagnetite is only possible with a complex of up-to-date instrumental methods