The economic interest in natural stones provides an interesting input to the study of coloured rock-forming minerals. Generally, the colour of a mineral is attributed either to the presence of intrinsically-coloured constituents or of trace elements substituting major elements in the crystallographic sites, or to physical factors such as crystal lattice defects. We have analysed the blue and blue-green silicate minerals dumortierite and amazonite, coming from Mozambique quartzites, and from Malawi and Brazil granitoids, respectively. This study was performed by a multiple analytical approach including (a) a comparison of different signals (optical light-polarized images, backscattered electron images and X-ray multielemental maps); and (b) a collection of quantitative data obtained by WDS systems for major elements, and by WDS and/or micro-PIXE facility for trace elements. A good correlation between Ti concentration zoning and pleochroism variations was observed in dumortierite. In addition, the blue dumortierite of Mozambique, with its unusual significant amounts of antimony (about 5 wt.% Sb2O3), represents a mineral with an intermediate composition between dumortierite and holtite. In amazonite the aquamarine colour seems to be related to the Pb content on the order of some hundreds of ppm.
Chemical investigation of coloured minerals in natural stones of commercial interest / Vaggelli, Gloria; Olmi, Filippo; Massi, Mirko; Giuntini, Lorenzo; Fedi, Mariaelena; Flora, Laura; Cossio, Roberto; Borghi, Alessandro. - In: MIKROCHIMICA ACTA. - ISSN 0026-3672. - ELETTRONICO. - 145:(2004), pp. 249-254. [10.1007/s00604-003-0162-6]
Chemical investigation of coloured minerals in natural stones of commercial interest
Massi, Mirko;Giuntini, Lorenzo;Fedi, Mariaelena;
2004
Abstract
The economic interest in natural stones provides an interesting input to the study of coloured rock-forming minerals. Generally, the colour of a mineral is attributed either to the presence of intrinsically-coloured constituents or of trace elements substituting major elements in the crystallographic sites, or to physical factors such as crystal lattice defects. We have analysed the blue and blue-green silicate minerals dumortierite and amazonite, coming from Mozambique quartzites, and from Malawi and Brazil granitoids, respectively. This study was performed by a multiple analytical approach including (a) a comparison of different signals (optical light-polarized images, backscattered electron images and X-ray multielemental maps); and (b) a collection of quantitative data obtained by WDS systems for major elements, and by WDS and/or micro-PIXE facility for trace elements. A good correlation between Ti concentration zoning and pleochroism variations was observed in dumortierite. In addition, the blue dumortierite of Mozambique, with its unusual significant amounts of antimony (about 5 wt.% Sb2O3), represents a mineral with an intermediate composition between dumortierite and holtite. In amazonite the aquamarine colour seems to be related to the Pb content on the order of some hundreds of ppm.I documenti in FLORE sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.