Beitrag
Uneven distribution of blue colour in kyanite
Ghera, Adriana; Graziani, Giorgio; Lucchesi, Sergio
Neues Jahrbuch für Mineralogie - Abhandlungen Band 155 Heft 2 (1986), p. 109 - 127
35 Literaturangaben
veröffentlicht: Oct 29, 1986
DOI: 10.1127/njma/155/1986/109
ArtNo. ESP154015502001, Preis: 29.00 €
Abstract
Various colourless and green kyanite samples were selected so as to obtain crystals characterized by the presence of a pale to deep blue colour zoning. The blue bands appear to be an aggregate of intensely coloured patches unevenly distributed in a colourless kyanite matrix. The distribution of minor elements content (Fe, Ti and Cr) was determined by electron microprobe on alignements crossing the blue bands along the [010] and [100] directions of each crystal. Variations in iron and titanium contents occur with variable intensity not only between the different samples but also among the numerous bands of each specimen, either for the two elements or for one of them. The optical absorption spectra recorded after heating in air at 1200 °C in each blue coloured specimen are characterized by the desappearance of the 16 500 cm-1 absorption band. This phenomenon suggests the setting of the oxidating conditions: Fe2+ → Fe3+ + e-. The heterogeneity of colouring may result from the great difficulty encountered by the chromophorous transition elements, notably Fe2+, in entering kyanite structure. This may produce deformations whose presence is suggested by X-ray diffraction investigations.
Schlagworte
Kyanite • colour zoning • chemical composition • thermal data • cell parameters • optical absorption spectra