Potential method of geobarometry using quartz

Abstract

As crystals grow from solution they may trap small amounts of the solvent and other solutes. It has long been known that minerals evolve gases on heating^1–4 and it has been assumed that, except for alteration during weathering, the gases are incorporated from the growth medium at the time of crystallisation. If the amount and composition of the gases trapped in minerals are to be used to make detailed geological interpretations it is essential that the location of the gas within the crystal structure is established. In minerals like carbonates and hydrates, ‘gases’ form part of the structure. Sites in which gas can occur include primary and secondary fluid inclusions, point defects, lattice dislocations, grain boundaries, and structure holes. Gas can also be adsorbed on crystal surfaces. Each site has its own characteristic temperature at which gas loss occurs, so that on heating a mineral the gases are released at different temperatures. This provides a method for distinguishing between gases from different sites.