On the Color and Genesis of Prase (Green Quartz) and Amethyst from the Island of Serifos, Cyclades, Greece

Klemme S, Berndt J, Mavrogonatos C, Flemetakis S, Baziotis I, Voudouris P, Xydous S.

Abstract

The color of quartz and other minerals can be either caused by defects in the crystal structureor by finely dispersed inclusions of other minerals within the crystals. In order to investigate themineral chemistry and genesis of the famous prase (green quartz) and amethyst association fromSerifos Island, Greece, we used electron microprobe analyses and oxygen isotope measurements ofquartz. We show that the color of these green quartz crystals is caused by small and acicular amphiboleinclusions. Our data also shows that there are two generations of amphibole inclusions within thegreen quartz crystals, which indicate that the fluid, from which both amphiboles and quartz havecrystallized, must have had a change in its chemical composition during the crystallization process.The electron microprobe data also suggests that traces of iron may be responsible for the amethystcoloration. Both quartz varieties are characterized by isotopic compositions that suggest mixing ofmagmatic and meteoric/marine fluids. The contribution of meteoric fluid is more significant in thefinal stages and reflects amethyst precipitation under more oxidizing conditions