I have been trying to model the mineral stability of a number of sodium phases found in the Eocene Green River Formation of Colorado, Utah, and Wyoming. The minerals are nahcolite (NaHCO3), Natron (Na2CO3), and Trona (Na2CO3•NaHCO3•2H2O). Data for all three are available, although in different databases. Once I copied some files across to a single database, I plotted the stability of the three phases, and compared it to recent data from Jagniecki, and others (Jagniecki, E.A., Lowenstein, T.K., Jenkins, D., and Demicco, R. V., 2015, Eocene atmospheric CO2 from the nahcolite proxy. Geology. v. 43, p. 1075-1078, doi:10.1130/G36886.1.). The two results show significantly different locations for the triple point at 1 atm total pressure, as shown below. The formation of large quantities of nahcolite in the Piceance Basin of Colorado at temperatures (from fluid inclusions) of 21-28°C are reasonable given the new triple point (the colored lines, where the gold line shows the reaction between nahcolite and trona at halite saturation. The triple point from existing data in GWB databases would require extreme CO2 activities equivalent to >3000 ppm atmospheric just to stabilize nahcolite at the low end of that temperature range. I would like to create new database entries using the data in the supplement to the cited paper. However, I am not especially well versed in the appropriate methods, and my thermodynamic training is more than 40 years behind me. I attach a table of various thermodynamic data from Robie and Hemingway (1995), from several of the available GWB databases, as well as from Jagniecki and others, 2015 (who cite Robie and Hemingway for nahcolite data).
I would also be interested in constructing similar database entries for analcime solid solutions of the formula NaAl (x)Si(3-x)O6•((3-x)/2)H2O. My last student had worked with another committee member to generate some of these, based upon the van't Hoff equation, but I find that these appear to reduce the stability of analcime from the entry in GWB, with a value of x=0.96, whereas data on Green River Formation analcime indicate values of x ranging from 0.75-0.95. The relative stability of the Na saline mineral above and authigenic Na-minerals analcime and dawsonite are important to understanding the evolution and character of Lake Uinta in which they were formed. Any help would be much appreciated.
NahcoliteTronaNatron Thermo data.xlsx
