Syntheses and Crystallization of Mineralogically Relevant Chalcogenide Glasses

Mineralogically relevant chalcogenide glasses with the composition Cu _x Bi ₅ Ag ₅ (As _0.33 S _0.335 Se _0.335 ) _90-x (x=2, 6, and 10, in mol%) that approximate the chemistry of some unusual sulfide mineral assemblages were synthesized. The differential thermal analyses revealed that the glass transition temperature (T _g ), onset crystallization temperature (T _c ), and peak temperature of crystallization (T _p ) first increase significantly with an increasing Cu content from 2 to 6 mol%, and then remain almost constant when the Cu content further increases to 10 mol%; the glass thermal stability also increases with an increasing Cu content. Both dry annealing and hydrothermal treatments were carried out in the temperature range of 207°-331°C for up to 96 h. X-ray diffraction analyses on annealed samples showed that dry annealing and hydrothermal treatments produced different phase assemblages. Dry annealing produced crystallized phases AgBiSe ₂ (bohdanowiczite), Cu ₂ Se (berzelianite), Ag ₃ AsS ₃ (xanconthite), Cu ₃ AsS ₄ (luzonite), AgBi ₃ S ₅ , and As ₄ CuS ₉ , while hydrothermal treatments produced phases AgBiSe ₂ (bohdanowiczite), AgBi ₃ S ₅ , and AgAsSe ₂ . This case study presents a new way for studying the formation and alteration of minerals in nature.