Hydrogen production in ultramafic, mafic and metamorphic rocks is limited by geochemical properties of rock and brine. These geochemical properties such as geochemical phases and molar compositions determine the maximum potential production of hydrogen from ultramafic rocks (resources). In this work, we use public geochemical data of ultramafic rocks from PetDB and in-house experiments (Ross et al., 2025) to evaluate variations in hydrogen resources at typical depths in the subsurface. We demonstrate a workflow for estimating hydrogen production from non-felsic igneous and metamorphic rocks that includes major oxide acquisition, mineral formula and endmember recalculation in MinplotX, and geochemical batch simulations of serpentinization across a range of hydrostatic pressures and geothermal temperatures. Our analysis indicates that the most optimal hydrogen production is at 10 km depth and forsterite composition below 0.9.

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