O występowaniu opali w rejonie Nasławic (Dolny Śląsk)

Abstract

ON OCCURRENCE OF OPALS IN THE NASŁAWICE REGION (LOWER SILESIA) Summary Mineralogical study of opals that occur near Nasławice (Lower Silesia) in the Gogołów-Jordanów serpentinite massif, has revealed their partical recrystallization. The opals are composed of colloidal silica and crystallites. Fe, Mn, Ni are colouring agents of the opals. Minor percentages of Co, Cu and Ca are also present as contaminants. The water content in the opals varies from 4,6 to 7 wt%. Water is released from opals in the range of 120-400°C. Opals from Nasławice are undoubledly the final products of low temperature alteration of minerals. High amounts of silica were released during the process of serpentinization.