On the origin of pseudoleucite from Cenozoic phonolite dyke from Loucna/Bohmisch Wiesenthal, Krušne hory/Erzgebirge Mts., Bohemia
Pivec, E.; Ulrych, J.; Langrová, A.
published: Jan 16, 2004
ArtNo. ESP154017903001, Price: 29.00 €
Euhedral (trapezohedral) pseudoleucite megacrysts and pseudoleucite aggregates occur in Cenozoic porphyritic phonolite. Pseudoleucite comprises aggregates of several components, the chief of which (8090% modal) is K-feldspar. Ba-rich sanidine (BaO = 1.61wt.%) has been partly replaced by disordered K-feldspar with a structural state intermediate between orthoclase and sanidine, and is preserved only in the orthoclase crystal cores. Minor components are dioctahedral 1M muscovite and relict analcime. The pseudoleucites are inferred to have grown in several stages: (1) Initial crystallization of leucite, (2) Transformation of leucite to analcime through reaction with sodium-rich fluids ("pseudoleucite reaction"), (3) An increase in PH2O then initiated the crystallization of K-feldspar at the expense of both leucite and analcime. The original (high-temperature) mineralogy and chemistry of both pseudoleucite and the host phonolite were subsequently strongly modified by late-stage hydrothermal processes.