Titre du document / Document title

Structural study of ellenbergerite. II: Effects of high pressure

Auteur(s) / Author(s)

COMODI P. ; ZANAZZI P. F. ;

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

Piazza univ., dip. sci. terra, 06100 Perugia, ITALIE

Résumé / Abstract

Compressibility and structural deformations induced by pressure in the high-pressure silicate ellenbergerite [Mg,(Ti,Zr),□]₂Mg₆(Al,Mg)₆(Si,P)₈O₂₈(OH)₁₀; hexagonal, space group P6₃, have been studied by single-crystal X-ray diffraction in a diamond anvil cell (DAC) in the pressure range 1 bar - 46 kbar. The bulk modulus of the mineral is 1330 kbar. The compressibility pattern is slightly anisotropic, with β_a = 2.4 10⁻⁴ and β_c = 3.1 10⁻⁴ kbar⁻¹. Compressibility is constant in the pressure range examined. Limited compositional differences of the samples do not produce significant variations in the compressibility coefficients. The geometrical data vs. pressure fit along the linear trends: a = a₀ - 0.0029 P c = c₀ - 0.0015 P with P in kbar and a and c in Å. In agreement with its occurrence in coesite-bearing rocks, ellenbergerite is a very dense phase, with a structure formed by chains of face-sharing octahedra, which represent rigid structural moduli. Therefore the structural response to the high pressure applied in the DAC consists of small deformations in octahedral bond lengths and angles, with only minor interpolyhedral geometrical variations. Comparison between high-pressure and high-temperature data indicates that the unit cell and bond geometry of ellenbergerite at formation conditions, namely 700-800°C and 25-30 kbar, do not differ greatly from those at room conditions

Revue / Journal Title

European journal of mineralogy   ISSN 0935-1221 

Source / Source

1993, vol. 5, n^o5, pp. 831-838 (24 ref.)

Langue / Language

Anglais

Editeur / Publisher

Schweizerbart, Stuttgart, ALLEMAGNE  (1989) (Revue)

Mots-clés anglais / English Keywords

compressibility ; experimental studies ; high pressure ; nesosilicates ; deformation ; X-ray diffraction analysis ; crystal structure ; anisotropy ; cell dimensions ; high-grade metamorphism ; Western Alps ; quartzites ; atomic packing ; coordination ; bonding ; unit cell ; stability ; distortion ; metamorphic rocks ;

Mots-clés français / French Keywords

Compressibilité ; Expérience ; Haute pression ; Nésosilicate ; Déformation ; Diffraction RX ; Structure cristalline ; Anisotropie ; Constante réticulaire ; Métamorphisme fort ; Alpes Occidentales ; Quartzite ; Empilement atome ; Coordinence ; Liaison interatomique ; Maille élémentaire ; Stabilité ; Distorsion ; Ellenbergerite ; Massif Dora Maira ; Massifs Cristallins Internes ; Roche métamorphique ;

Mots-clés espagnols / Spanish Keywords

Compresibilidad ; Experiencia ; Alta presión ; Difracción RX ; Estructura cristalina ; Anisotropía ; Constante reticular ; Metamorfismo fuerte ; Alpes Occidentales ; Cuarzita ; Estructura átomo ; Coordinancia ; Enlace interatómico ; Celdilla cristalina ; Estabilidad ; Distorsión ; Roca metamórfica ;

Localisation / Location

INIST-CNRS, Cote INIST : 519, 35400004784360.0030