Am Mineral 69:449–457Īgeeva OA (1999) Typomorphism of accessory lomonosovite from rocks of Khibiny massif. Metasomatism occurred at high temperature the gigantic apatite deposits of the Khibiny massif seem to be related to this metasomatic event.Ībbott RN Jr (1984) KAlSiO 4 stuffed derivatives of tridymite: phase relationships. The metasomatic nature of the transformation of urtites to rischorrites is identified from massive introduction of potassium and silica and removal of sodium. The presence of relic nepheline within intergrowth domains and the successive replacement of precursor nepheline by alkali feldspar and associated formation of feldspar-feldspathoid intergrowth suggest development of the rischorrites from feldspar urtites, in which nepheline is the dominant felsic phase. The most frequently observed orientation relation is the parallel orientation of the kalsilite and nepheline directions with the direction of the alkali feldspar host and concomitant coincidence of the feldspathoid directions with the -, - and directions of the alkali feldspar. Strict crystallographic orientation relations were identified among the intergrowth phases based on optical investigation using a 4-axes universal stage and crystal orientation imaging using electron back scatter diffraction. Poikilitic megacrysts of alkali feldspar with abundant inclusions of feldspar-nepheline and feldspar-kalsilite micrographic or lamellar intergrowths are characteristic for the rischorrites of the Khibiny massif.
0 kommentar(er)
