Titre du document / Document 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

Auteur(s) / Author(s)

WERDING G. ; SCHREYER W. ;

Affiliation(s) du ou des auteurs / Author(s) Affiliation(s)

Ruhr-Univ. Bochum, Inst. Mineralogie, 4630 Bochum, ALLEMAGNE

Résumé / Abstract

The pur Mg end member of the newly discovered mineral werdingite with the ideal formula Mg₂Al₁₄Si₄B₄O₃₇ was synthesized with 100% yields at 4-7 kbar, 800-875°C employing dried B₂O₃ and a fired gel of the MgAl-silicate composition. Under these conditions it also grew from an anhydrous mixture of synthetic Mg-grandidierite, MgAl₃SiBO₉, and another new phase having the composition Al₈Si₂B₂O₁₉, thus suggesting that werdingite is a stable phase in the system MgO-Al₂O₃-B₂O₃-SiO₂. Mg-werdingite is triclinic with a_o = 7.993(3); b_o = 80150(2); c_o = 11.388(4) Å; α = 110.45(2)°, β = 110.88(2)°; γ = 84.62(2)°. Together with grandidierite, Al₈Si²B₂O₁₉, 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 (<10kbar). At lower temperatures it breaks down, in the presence of water, to form Mg-grandidierite + corundum + the tourmaline phase □Mg₂Al₇Si₆B₃O₂₇(OH)₄. Approximating anhydrous conditions, the breakdown products of Mg-werdingite at high pressures (>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 B₂O₃ contents

Revue / Journal Title

European journal of mineralogy   ISSN 0935-1221 

Source / Source

1992, vol. 4, n^o1, pp. 193-207 (22 ref.)

Langue / Language

Anglais

Editeur / Publisher

Schweizerbart, Stuttgart, ALLEMAGNE  (1989) (Revue)

Mots-clés anglais / English Keywords

borosilicates ; stability ; experimental studies ; synthesis ; formula ; P-T conditions ; mineral assemblages ; symmetry ; unit cell ; cell dimensions ; crystal structure ; transformations ; granulite facies ; SEM data ; infrared spectra ; X-ray diffraction analysis ; X-ray powder diffraction ;

Mots-clés français / French Keywords

Borosilicate ; Stabilité ; Expérience ; Synthèse ; Formule ; Condition pression température ; Association minérale ; Symétrie ; Maille élémentaire ; Constante réticulaire ; Structure cristalline ; Transformation ; Faciès granulite ; Donnée MEB ; spectre IR ; Diffraction RX ; Diagramme poudre ; Werdingite ;

Mots-clés espagnols / Spanish Keywords

Borosilicato ; Estabilidad ; Experiencia ; Síntesis ; Fórmula ; Condición PT ; Asociación mineral ; Simetría ; Celdilla cristalina ; Constante reticular ; Estructura cristalina ; Transformación ; Facies granulita ; Dato MEB ; Espectro IR ; Difracción RX ; Diagrama polvo ;

Localisation / Location

INIST-CNRS, Cote INIST : 519, 35400002321652.0150