Bibliographie complète

The Jabal Nafusah phonolites are characterized by the dominance of felsic components, or a very low colour ratio. As mentioned by Almond et al. (1974), phenocrysts (mostly of alkali feldspar) may occur, but generally the phonolites are fine grained, poorly crystallized or even aphyric. Along with microscope analysis, the mineralogical composition has been investigated, essentially by means of X-ray diffraction. The chief (felsic) components found were: sanidine, analcime, nepheline, sodalite and albite (given in order of approximately decreasing frequency). The frequency of analcime is quite remarkable, and has not been hitherto described. Also shown are the relations of changing proportions of mineralogical compositions and detailed X-ray data.