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During systematic characterization of amphiboles that still lack a complete mineral description, fluoro-tremolite was identified in a specimen from the Limecrest-Southdown quarry, Sparta, New Jersey, USA, which was provided by the Franklin Mineral Museum. The ideal formula of fluoro-tremolite isA□BCa2CMg5TSi8O22WF2and the empirical formula derived for the holotype specimen, based on the results of electron-microprobe analysis and single-crystal structure refinement, isA(Na0.28K0.02)Σ0.30B(Ca1.99Na0.01)Σ2.00C(Mg4.70${\rm Fe}_{{\rm 0}{\rm. 28}}^{{\rm 2 +}} $Zn0.01${\rm Ti}_{{\rm 0}{\rm. 01}}^{{\rm 4 +}} $)Σ5.00T(Si7.68Al0.32)Σ8.00O22W(F1.16OH0.84)Σ2.00.The unit-cell dimensions in space groupC2/marea= 9.846(2),b= 18.050(3),c= 5.2769(14) Å, β = 104.80(2)° andV= 906.7 (3) Å3andZ= 2; thea:b:cratio is 0.545:1:0.292. Fluoro-tremolite is biaxial (+), with α = 1.5987(5), β = 1.6102(5), γ = 1.6257(5), 2V(meas.) = 85(1)oand 2V(calc.) = 82o. The strongest ten reflections in the powder X-ray pattern [dvalues (in Å),I, (hkl)] are: 2.706, 100, (151); 3.126, 67, (310); 2.531, 59, ($\bar 2$02); 3.381, 57, (131); 2.940, 43, ($\bar 1$51, 221); 3.276, 37, (240); 2.337, 36, ($\bar 3$51); 2.592, 35, (061); 2.731, 34, ($\bar 3$31); 2.163, 34, (261). Both the mineral and the mineral name have been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA2016–018); the holotype has been deposited at the Franklin Mineral Museum (32 Evans Street, Franklin, 07416 New Jersey, US), under the catalogue number 7710.Comparison with new data on tremolite and synthetic fluoro-tremolite provides a more sound crystal-chemical model of the end-member compositions and their solid-solution.

In this work, we address the intensity evolution of the CO2 FTIR bands of cordierite as a function of increasing T, by comparing data obtained from in situ versus quenching measurements. A natural well-characterized cordierite from Kragero (Arendal region, Norway) was studied up to 1200 °C using a heating stage fitted on a FTIR microscope. Two different oriented sections (001) and (010), respectively, were examined in order to check for the effect of the channel orientation on the CO2 release from the matrix. Spectra collected in situ show that increasing temperatures induces an increase in peak width for all CO2-related bands. The effects on the integrated absorbance A i are different for the different modes. Most notably, the integrated intensity A i of the anti-symmetric stretching mode (ν3) increases significantly up to 800 °C and then progressively decreases to 1000/1200 °C, depending on the sample orientation. Data obtained on quenched samples reveal that there is no variation in the band intensity for T

In this study, we describe the first FTIR measurements of CO2 desorption from cordierite, a microporous mineral stable up to high T conditions. To this purpose, we collected isothermal heating data on several (001) oriented sections of a well-characterized CO2-rich sample. Single-crystal slabs were heat-treated up to 1000 °C, and the intensity of the ν 3 antisymmetric stretching mode of CO2 at 2348 cm−1 was monitored as a function of time. The experimental data were modeled by using the mono-dimensional plane-sheet diffusion formalism; diffusion coefficients were plotted in the Arrhenius space and activation energies were calculated. Final data are as follows: −logD 0 = 4.2 ± 0.5 m2/s and E a = 208 ± 11 kJ/mol. Comparison with diffusion data from the literature (Lepezin and Osorgin in Rossijskaa Akademia Nauk 339:658–661, 1994) shows that at 800 °C H2O diffuses almost two orders of magnitude faster than CO2 along the structural channels of cordierite, with the difference in diffusion coefficients increasing at lower temperatures, and this implies that at lower temperatures H2O mobility is more favored compared to CO2. Therefore, the volatile contents measured in exhumed rocks may not reflect the H2O/CO2 ratio upon cordierite crystallization, and this could significantly affect the thermodynamic calculations for fluid activities or peak metamorphic conditions.

The crystal chemistry of sekaninaite from Dolní Bory, Czech Republic, was characterized by a multimethod approach. Particular emphasis was put on the characterization of the channel constituents (i.e. H2O and CO2). Electron microprobe analysis shows the sample to be close to the Fe endmember [XFe = Fe/(Fe+Mg) = 94%) with significant Mn (1.48 wt.%) present; laser ablation mass-spectrometry showed the presence of 0.42 wt.% Li2O. H2O and CO2 contents (1.48 and 0.17 wt.%, respectively) were determined via secondary-ion mass-spectrometry. Sample homogeneity was checked by Fourier-transform infrared (FTIR) imaging using a microscope equipped with a focal plane array detector. Single-crystal FTIR spectroscopy confirmed the presence of two types of H2O groups in different orientations (with prevalence of the type II orientation), and that CO2 is oriented preferentially normal to the crystallographic c axis. Using the Beer-Lambert relation, integrated molar coefficients, εi, were calculated for both types of H2O (εi H2O[I] = 6000±2000; εi H2O[II] = 13000±1000) and for CO2 (εiCO2 = 2000±1000).