Obsidian hydration dating lab
Still others, however, are called incompatible because they are incompatible with the solid phases and are concentrated in the liquid.This incompatibility may be due to the ions being too large for the available ionic sites in the liquid, such as with rubidium (Rb), cesium (Cs), strontium (Sr), and barium (Ba). Picrite 2%), perlitic and/or vitrophyric fabric may form in the glass.In peralkaline melts, barium and strontium are rapidly depleted by feldspars, while zirconium and niobium continue to be enriched to relatively high levels. Most glass that is technically obsidian, but useless for tool production was extruded as vitrophyre or tuff, or subsequently hydrated to form perlite (see Shackley 1988). At low temperatures, a mixture of crystals is always more stable than a glass, and glasses will crystallize spontaneously if the atoms present have an opportunity to diffuse through the glass and become ordered (Cann 1983).This seems to have been the case with the San Francisco Peak glass where the formation of zircons absorbed the zirconium and feldspars absorbed the strontium (Burton 1986). In order to produce aphyric, vitreous obsidian, the melt must have contained either a very low water content, or it must have been degassed in some way before eruption (Cann 1983; Cox et al. This can occur if the glass is reheated, or by hot water percolating through the glass dissolving and reprecipitating atoms and compounds. dissertation, Department of Anthropology, Tulane University. Research questions focus on the relationship between natural resources, settlement patterns, and ancient production and distribution systems. The work presents the results of survey and excavations in a 138 km2 area surrounding an important obsidian source.
"Evolved" obsidian magmas may contain these crystal "hosts" and the ratio of a given element between the liquid and solid phases will change dramatically. Unfortunately for flaked tool production, most liquids rich in glass formers are also rich in water and other volatiles.
These, and others, are called compatible elements because they are compatible with the crystallizing solids.
Others (gallium and germanium) are evenly distributed between the solid and liquid phases.
Two factors control whether a magma (melt) will form a glass, the rate of cooling and its viscosity, which is determined by its chemical composition. Mount Elden and RS Hill in the San Francisco Volcanic Field, and many of the lesser known domes at Los Vidrios are classic examples of rhyolite dome structures (Nations and Stump 1981).
While it is theoretically possible to form a glass from most lavas, the presence of aluminum and silicon oxides in rhyolite greatly facilitates the process (Cann 1983; Cox et al. Classification scheme for volcanic rocks based on alkali element and silica content.