Can AlphaMELTS simulate the formation of spodumene?

[liushanke]

Hi everyone,

I'm trying to figure out if AlphaMELTS can be used to model the crystallization of spodumene (LiAlSi₂O₆) from a lithium-rich melt, such as in a pegmatite system. I understand that AlphaMELTS relies on the MELTS thermodynamic database, but I'm unsure if it includes sufficient data for lithium-bearing minerals like spodumene.

Alternatively, if spodumene isn't well-supported in the MELTS database, are there any workarounds or additional tools you'd recommend?

Any insights or experiences would be greatly appreciated! Thanks in advance!

Regards, Shanke

[Paula]

There aren't any Li-bearing species in the main MELTS thermodynamic database. We did fit some Li-bearing end members with the MELTS / Berman formulation a few years back, including alpha and beta spodumene, and Li₂SO₃ solid and liquid. To calibrate the interaction parameters between Li₂SO₃ liquid and the other MELTS liquid end members would require some experimental data for coexisting melt and Li-bearing phases though.

I just checked LEPR (lepr.earthchem.org) and there are no spodumene analyses there. There's minor amounts of LiO₂ in cordierite and amphibole but neither of those phases are well-modeled in MELTS. Do you know of any experimental studies where compositions are analyzed for all coexisting phases, both solid and liquid? We could get them queued for inclusion in LEPR.

Paula

[liushanke]

Hi Paula, 
Thanks for your message! It's interesting to hear about the work you've done fitting Li-bearing end members like alpha and beta spodumene, as well as Li₂SO₃, into the MELTS formulation. I can see how the lack of interaction parameters for Li₂SO₃ liquid with other MELTS liquid end members would be a challenge without experimental data on coexisting melts and Li-bearing phases. 
I've recently come across some thermodynamic data for spodumene (both α- and β-forms) and lepidolite from Google search (Spodumene:https://journals.sagepub.com/doi/abs/10.1080/25726641.2020.1827675;https://www.mdpi.com/2075-163X/10/6/519. Lepiodlite:https://www.sciencedirect.com/science/article/pii/S0040603105002418), though I'm not sure if they include full compositional analyses of coexisting solid and liquid phases from experimental studies. However, these seem more focused on the solid phases rather than melt compositions.  I'd be happy to keep an eye out for experimental studies that report compositions of all coexisting phases (solid and liquid) during my regular literature searches. If I find anything relevant—especially with spodumene or other Li-bearing phases like lepidolite—I'll let you know so we can consider queuing them for inclusion in LEPR.
Regards, Shanke