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Beryllium is a significant constituent in sapphirine in some metamorphic and pegmatitic rocks, and thus could have a major effect on its stability relationships. Using the stoichiometries of reactions involving sapphirine and associated phases in the MgO-BeO-Al 2 O 3 -SiO 2  (MBeAS) system in conjunction with molar volume data, we have plotted maps of the sapphirine solid-solution field in both μ-μ and μ-P space, where μ is the chemical potential of an exchange component such as (BeSi)(AlAl)-1. These maps give a pressure sequence of stable MBeAS univariant reactions and divariant assemblages that are consistent with experimental data, e.g., they show how Be stabilizes sapphirine + forsterite, which is rare in nature but readily synthesized over a wide P-T range in the presence of Be. We generate a MBeAS petrogenetic grid for sapphirine-bearing assemblages over the approximate range T = 700-900 °C, P = 0-2.5 GPa, identify divariant and univariant assemblages containing sapphirine with maximum Be, and determine the sense of variation of maximum Be content with P. At lower T, maximum Be occurs at the low-P limit of surinamite stability, ca. 0.5 GPa. At higher T, maximum Be increases with P, following the MBeAS univariant reactions involving (sapphirine + surinamite + orthopyroxene + chrysoberyl + forsterite or spinel).

american mineralogist

Synthesis of beryllian sapphirine in the system MgO-BeO-Al 2 O 3 -SiO 2 -H 2 O and comparison with naturally occurring beryllian sapphirine and khmaralite, Part 2: A chemographic study of Be content as a function of P, T, assemblage and FeMg –1 exchange