Bazalt z Graczy i towarzyszące mu utwory piroklastyczne

Abstract

BASALT FROM GRACZE AND ITS ACCOMPANYING PYROCLASTIC FORMATIONS

Summary

Basaltic intrusion that occurs at Gracze, near Niemodlin, Lower Silesia (Fig. 1), consists of basalt and of accompanying volcanic formations (Fig. 2). The basaltic intrusion consists here of augite, olivine, nepheline, magnetite and of small amounts of plagioclase and volcanic glass. The cover under examination reveals certain changes in mineral composition related to gravitational differentiation of magma. As concerns its chemical composition, the basaltic intrusion is characterized by an insufficient amount of silica and by a considerable quantity of sodium. Thus, it belongs to type alkaline basalts. Breccias that accompany the basaltic intrusion consist of lapilli and of marly detached blocks cemented with devitrified glassy mass. These formations are partly altered, montmorillonite being their final product of alteration. As compared with the basalt intrusion, the breccias are characterized by a greater amount of silica. The lapilli found to occur in the breccia are, in their chemical composition, similar to rhyobasalt. Among other mineral compounds anorthoclase occurs, as well.