Microstructures in Two Alkali Feldspar Megacrysts from the Papuk Mt., Croatia

Abstract

Two types of megacrysts, one from Pakra Creek and the other from the Sloboština Creek locality proved to be low microcline in associationwith low albite and quartz. A sample from Pakra Creek is a vein filling megacryst characterised by the absence of twinning. The deduced crystallization temperature is below 460°C. The sample from Sloboština Creek is a pocket forming megacryst which shows tweed-like texture, with deduced crystallization temperature near to but above 460°C. Both samples are characterized by a continuously modulated lattice on the submicroscopic scale.