Cation exchange experiments between gem quality sanidine [Formula: see text] and KCl melt produced chemical alteration of alkali feldspar starting at the grain surface and propagating inwards by highly anisotropic Na-K interdiffusion on the alkali sublattice. Diffusion fronts developing in b-direction are very sharp, while diffusion fronts within the a-c-plane are comparatively broad. Due to th...

A significant tin deposit has been identified in the northeast part of the Late Proterozoic Arabian Shield. Cassiterite-topaz-quartz greisens are distributed over 16 km2 in flat-topped cupolas of a highly evolved, zinnwaldite-bearing alkali-feldspar granite which composes part of the silsilah ring complex (lat 26"06'N, long 4240'E). The 587 m.y. old alkali-feldspar granite is overlain by a cara...

Phase relations at atmospheric pressure in the pseudobinary join KA1Si206 (Lc)NaA1Si3Os(Ab) and in the pseudoternary join Lc-Ab-CaA12Si2Os(An) indicate that leucite is incompatible with Na-feldspar. In the former join leucite can exist with an alkali feldspar of maximum albite content Ab54. In the Lc-Ab--An join, leucite only coexists with ternary feldspars with high An contents (approximately ...

The central pluton within the Neoproterozoic Katharina Ring Complex (area of Gebel Mussa, traditionally believed to be the biblical Mt. Sinai) shows a vertical compositional zoning: syenogranite makes up the bulk of the pluton and grades upwards to alkalifeldspar granites. The latters form two horizontal subzones, an albite–alkali feldspar (Ab–Afs) granite and an uppermost perthite granite. The...

The usage of “potassium feldspar” and “alkali has been confused in earth sciences for a long time. term is the solid solution series between two components KAlSi3O8 (potassium feldspar) NaAlSi3O8 (sodium feldspar), including more or less CaAl2Si2O8 (lime as third component. practice an end member feldspar solution. At present, scientific appropriate terms without confusion needed sciences. This...

105 Abstract: Origin of A-type alkali feldspar granites is currently the subject of a world-wide debate. Contrasting hypotheses have been proposed, which range from an entirely crustal origin to an almost complete mantle derivation. A-type alkali feldspar granites belong to either unimodal granite (rhyolite)-dominated association, or bimodal gabbro (basalt)-granite (rhyolite) suite. It is argue...

Mineral dusts originating from Earth's crust are known to be important atmospheric ice nuclei. In agreement with earlier studies, feldspar was found as the most active of the tested natural mineral dusts. Here we investigated in closer detail the reasons for its activity and the difference in the activity of the different feldspars. Conclusions are drawn from scanning electron microscopy, X-ray...