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For thirty-five years (Griffin et al., 1989) it has been possible to extract useful temperature estimates for peridotitic pyrope-rich garnet from the lithospheric mantle using the Nickel-in-garnet method. There have been amendments (Ryan et al., 1996; Canil et al., 1999; Nimis et al., 2024) to determine the best calibration but, overall, this method has proven to be a practical tool. Contrasting with thermometry, barometry in single peridotite pyrope crystals is underdeveloped. Cr-in-Grt barometry is the most disseminated method for estimating P from garnet separate, but Cr-in-Grt provides only minimum constraints on P from all but (rare) extremely depleted garnet compositions. Because of this, without additional constraints, it is not possible to determine whether a particular garnet xenocryst comes from the diamond stability field, or to construct reliable geotherms from garnet separate.

To extract P, scientists use several workarounds; such as by making educated guesses of P by projecting garnet Ni-in-Grt T onto known regional geotherms. And by relying only on Cr-in-Grt pressure estimates from ultra-depleted garnet. However, assumed geotherms may not always be valid, especially for very old pipes, and fully Cr-saturated garnet are rare at best, and absent in many kimberlite pipes. The current stateof-the-art in peridotitic garnet barometry is, therefore, unsatisfying; particularly as garnet is an ideal mineral for single-crystal methods–occurring in both depleted and fertile compositions, in both the graphite and diamond stability fields, abundantly in kimberlite separate and derived alluvium, and included in diamond.