La saliotite, interstratifié régulier 1:1 cookéite/paragonite. Nouveau phyllosilicate du métamorphisme de haute pression et basse température
Goffé, Bruno; Baronnet, Alain; Morin, Guillaume
European Journal of Mineralogy Volume 6 Number 6 (1994), p. 897 - 912
published: Nov 30, 1994
manuscript accepted: Jun 30, 1994
manuscript received: Mar 24, 1994
ArtNo. ESP147050606016, Price: 29.00 €
Abstract Saliotite has been found in Permo-Triassic metapelites of the Alpujarrides nappes in the Sierra Alhamilla (Betic Chain, Andalusia, S.E. Spain). It occurs in schists as deformed lamellae, intergrown with pyrophyllite, paragonite, cookeite, and calcite including relics of aragonite. Saliotite is optically biaxal negative, 1.58 < nα < 1.59, 1.58 < nβ < 1.59, 1.59 < nγ < 1.6, Δ = 0.007, 2V = 30-50o(obs.). Based on electron and ion microprobe analyses the empirical formula is Si3.1Al3.8Mg0.01Fe0.03Ca0.02K0.04 Na0.41Li0.5O9.86(OH)5, corresponding to the ideal formula: [Si3Al]Al3Li0.5Na0.5O10(OH)5. The unit-cell is monoclinic with a = 5.158(1), b = 8.914(3), c = 23.83(2) ., β = 94.23(4)°, V = 1093(1) Å3, Z = 4. The calculated density is 2.75 g/cm3. The strongest diffraction lines in the X-ray oriented powder pattern are: (dÅ/l/hkl) 23.76/60/001; 11.89/40/002; 7.93/30/003; 4.75/80/005; 3.396/100/007; 2.966/50/008. Transmission electron microscopy confirms the nature of a perfectly regular 1:1 ordered interstratification (R = 1) of cookeite (di-trioctahedral chlorite, 14 Å) and paragonite (dioctahedral mica 9.5 Å). The saliotite polytype is 1M. At the hundred-. scale, saliotite is mainly intergrown with lamellae of cookeite and less frequently with paragonite. Saliotite is a metamorphic rock-forming mineral. The deformation of saliotite in the main metamorphic foliation, its inclusion in calcite veins containing relics of aragonite, and the widespread crystallisation of cookeite and paragonite in the late metamorphic structures demonstrate the early crystallisation of saliotite during the high-pressure metamorphic stage. The P-T conditions of saliotite stability are estimated around 280-330°C and 8 kbar on the basis of aragonite-, ferrocarpholite-, and pyrophyllite-bearing assemblages.