The formation of silicic glasses (obsidian) is essentially a rare event in nature since a number of limiting factors must occur in order to form a glass.
A brief discussion of rhyolite equilibrium melt reactions will be useful for the understanding of the occurrence of obsidian in the Southwest.
Explain if the instrument appears to be calibrated based on the data you obtained for the Low Calibration Standard.
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.
Rubidium isotope would be the best isotope to use for that measurement because it contains the most years that would be needed to measure that span.
Even with the help of this isotope the task would still be rather difficult to make precise.
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.