High-temperature ammonium white mica from the Betic Cordillera (Spain)

Abstract

High-temperature, ammonium-rich white mica has been identified for the first time in deep Paleozoic (and probably older) polymetamorphic schists from the Internal Zone of the Betic Cordillera (Spain). Ammonium-rich white mica has been characterized by optical microscopy, X-ray diffraction, infrared spectroscopy, elemental analysis, electron microprobe, and scanning and transmission electron microscopy. High-temperature, ammonium-rich white mica shows some significant chemical differences with tobelite formed in hydrothermal and low-temperature metamorphic rocks. Although the average formula, Ca 0.09 Na 0.01 K 0.15 (NH 4 ) 0.75 (Al 1.70 Ti 0.01 Fe 0.26 Mg 0.13 )(Si 2.99 Al 1.01 )O 10 (OH) 2 , is typical of a dioctahedral mica, the chemical plots reveal a clear deviation toward the trioctahedral field. Thus, the increase in Fe + Mg contents is not accompanied by the parallel increase of Si contents, characteristic of the phengitic substitution, which is characteristic of low-pressure conditions of formation. Chemical differences are also accompanied by notable differences in the optical properties, both features suggesting that the term tobelite is not appropriate for this mica. Ammonium-rich white mica relics only persist in some graphite-rich microdomains, defining the first schistosity. Textural relations indicate that this mica formed during an older pre-Alpine metamorphic episode.

Ambient and cold‐temperature infrared spectra and XRD patterns of ammoniated phyllosilicates and carbonaceous chondrite meteorites relevant to Ceres and other solar system bodies

“…), and ammoniated illites and micas, especially from hydrothermal or metamorphic zones near organic‐rich rocks (e.g., Sucha et al. ; Nieto ; Ruiz Cruz and Sanz de Galdeano ). In many of these cases, decomposition of organic material supplied the nitrogen for ammonia incorporation in the mineral structure.…”

Exsolution Microstructures in Nh4-Bearing Muscovite and Annite in Gneisses From the Torrox Area, Betic Cordillera, Spain

“…A complete description of the methodology used can be found in Ruiz Cruz & Sanz de Galdeano (2008Galdeano ( , 2009. Samples were systematically studied by petrographic microscopy, X-ray diffraction (XRD), X-ray energy-dispersive (EDS) system, and elemental analysis.…”

“…These analyses are hindered by the rapid volatilization of NH 4 , although this effect is considerably less pronounced in Ann than in the dioctahedral mica (Ruiz Cruz & Sanz de Galdeano 2008, 2009. Results of some analyses of Ms and Ann, obtained in grains with coarse lamellae of Ann (grains shown in Fig.…”

“…The discovery of high-temperature NH 4 -rich dioctahedral mica (tobelite) in most mica schists overlying the gneissic formations (Ruiz Cruz & Sanz de Galdeano 2008), and of a new NH 4 -rich trioctahedral annitelike species (suhailite) in more restricted areas (Ruiz Cruz & Sanz de Galdeano 2009), led us to perform a detailed study of the gneissic rocks from the Torrox area, where a clear transition from schists to gneisses is observed, with two main objectives: 1) a test of the evolution of NH 4 -bearing mica at the passage from the less metamorphosed schists to the more intensely metamorphosed gneissic formations, and 2) a detailed study of the composition of the several generations of micas in the gneissic rocks in order to establish their metamorphic evolution, taking into account the fact that ammonium-bearing micas had not been previously identified in these terranes. The NH 4 -rich dioctahedral mica appears as scarce relics, widely replaced by muscovite and annite, and is characterized by high Fe+Mg contents, which are not coupled with a parallel increase in Si, characteristic of the phengitic micas.…”

Coexisting nanoscale phases of K-illite, NH4,K-illite and NH4-illite-smectite: an organic nitrogen contribution in the hydrothermal system of Harghita Bãi, East Carpathians, Romania

“…In very-low-grade metapelites from the Douro-Beira Carboniferous basin in Portugal, Nieto (2002) described the NH 4 -and K-micas segregated into well-separated packets with few interstratifications. In addition, the NH 4 -bearing mica layers intergrown with K-mica layers were identified in lowgrade metaclastic rocks and polymetamorphic schists from the Betic Cordillera (Ruiz-Cruz & Sanz de Galdeano, 2008Galdeano, , 2010. X-ray diffraction (XRD) is an accurate method for detecting the interstratifications between NH 4 -I and other 2:1 layer types such as K-I, smectite or vermiculite (Drits et al, 1997a).…”