Title: Synthesis and stability of werdingite, a new phase in the system MgO - Al2O3 - B2O3 - SiO2 (MABS), and another new phase in the ABS-system
Abstract: The pur Mg end member of the newly discovered mineral werdingite with the ideal formula Mg 2 Al 14 Si 4 B 4 O 37 was synthesized with 100% yields at 4-7 kbar, 800-875°C employing dried B 2 O 3 and a fired gel of the MgAl-silicate composition. Under these conditions it also grew from an anhydrous mixture of synthetic Mg-grandidierite, MgAl 3 SiBO 9 , and another new phase having the composition Al 8 Si 2 B 2 O 19 , thus suggesting that werdingite is a stable phase in the system MgO-Al 2 O 3 -B 2 O 3 -SiO 2 . Mg-werdingite is triclinic with a o = 7.993(3); b o = 80150(2); c o = 11.388(4) A; α = 110.45(2)°, β = 110.88(2)°; γ = 84.62(2)°. Together with grandidierite, Al 8 Si 2 B 2 O 19 , mullite, and at least two Al-borates, werdingite belongs to a family of phases that are structural derivatives of sillimanite.Mg-werdingite is stable only at high temperatures (>800°C) and low to intermediate pressure ( 10 kbar) are sinhalite + corundum + dumortierite. This type of stability is in agreement with the occurence of Fe-bearing natural werdingite in an anhydrous granulite-facies environments as well as an alternative to the assemblage dumortierite + corundum with higher B 2 O 3 contents
Publication Year: 1992
Publication Date: 1992-02-13
Language: en
Type: article
Indexed In: ['crossref']
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Cited By Count: 26
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