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Characterization of smectite to NH (sub 4) -illite conversion series in the fossil hydrothermal system of Harghita Bai, east Carpathians, Romania

Iuliu Bobos
Characterization of smectite to NH (sub 4) -illite conversion series in the fossil hydrothermal system of Harghita Bai, east Carpathians, Romania
American Mineralogist (May 2012) 97 (5-6): 962-982

Abstract

Ammonium-illite (NH (sub 4) -I) is one of the alteration products present in a breccia structure in the fossil hydrothermal system from Harghita Bai (East Carpathians), Romania. A series from smectite (S) via ordered interstratified structures to NH (sub 4) -I (40 to 5%S) was characterized by X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FTIR), scanning and transmission electron microscopy (SEM and TEM), and chemical analyses. Calculation of one-dimensional X-ray patterns was simulated with the NEWMOD code. Transition from two- to one-water smectite interlayer was identified by XRD. Selected samples were saturated with K (super +) -, Mg (super 2+) -, and Li (super +) -cations to differentiate low- to high-charge smectite or beidelite layers. X-ray patterns of random powders of K (super +) -saturated samples, heated at 300 degrees C show a transition from 1Md to cis- and trans-vacant 1M polytype. The cell parameters of the cis-vacant and trans-vacant 1M polytype were calculated by oblique texture electron diffraction. The vibration frequencies at 1430 cm (super -1) of the N-H bond were identified in the samples analyzed. Scanning and transmission electron microscopy images show morphological changes from flaky to lath-like shapes. The mean shape ratio of lath crystals ranges from 6 to 5.42 nm and the mean area from 7.8 to 24X10 (super 4) nm (super 2) . The mean thickness of the NH (sub 4) -I layers ranges from 4.62 to 7.89 nm. The calculated structural formula of end-member NH (sub 4) -I (5%S) is: [(NH (sub 4) (super +) ) (sub 0.66) K (sub 0.10) (super +) Na (sub 0.01) (super +) Sr (sub 0.02) (super 2+) ] (sub 0.81) (Al (sub 1.85) (super 3+) Fe (sub 0.01) (super 3+) Mg (sub 0.15) (super 2+) ) (sub 2.01) (Si (sub 3.30) (super 4+) Al (sub 0.70) (super 3+) ) (sub 4.00) O (sub 10) (OH) (sub 2) . The fixed NH (sub 4) (super +) content quantified ranges from 0.39 to 0.66 atoms per half unit cell [O (sub 10) (OH) (sub 2) ]. Tetrahedral and octahedral substitutions took place as the %S decreases. The NH (sub 4) -I-S series formed via direct precipitation from solution at different temperatures.


ISSN: 0003-004X
EISSN: 1945-3027
Coden: AMMIAY
Serial Title: American Mineralogist
Serial Volume: 97
Serial Issue: 5-6
Title: Characterization of smectite to NH (sub 4) -illite conversion series in the fossil hydrothermal system of Harghita Bai, east Carpathians, Romania
Author(s): Bobos, Iuliu
Affiliation: University of Oporto, Faculty of Sciences, Oporto, Portugal
Pages: 962-982
Published: 201205
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 122
Accession Number: 2012-056681
Categories: Mineralogy of silicatesSedimentary petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 4 tables
N46°00'00" - N49°49'60", E21°00'00" - E28°00'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Mineralogical Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201229
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