Mark S. Ghiorso

Microsoft EXCEL spreadsheet-based program for calculating equilibrium gas speciation in the C–O–H–S–Cl–F system ☆

Abstract A high-temperature gas is a relatively simple mixture of gas species in homogeneous equilibrium. Volcanic gases are composed of the elements C, O, H, S, Cl and F along with trace amounts of other components. We present an Microsoft EXCEL spread sheet and add-in for calculation of homogeneous equilibrium in this system. This EXCEL extension allows users to calculate equilibrium species fugacities at 1 bar for any volcanic or laboratory gas mixture in the C–O–H–S–Cl–F system. Homogeneous equilibrium is calculated using the RAND algorithm based on the assumption of ideal mixing of 66 molecular gas species. This is implemented as a hierarchy of class objects written in C++. This computation engine is compiled into a dynamically linked EXCEL add-in which can be accessed by any EXCEL spread sheet. An easy to use spread sheet is provided which implements this add-in.