Electron Microprobe Analysis and Scanning Electron Microscopy in Geology

An Excel spreadsheet to classify chemical analyses of amphiboles following the IMA 2012 recommendations

Infrared Spectroscopy of Minerals and Related Compounds

Spectroscopic studies of alkaline activated slag geopolymers

The titration of clay minerals II. Structure-based model and implications for clay reactivity.

Mid-IR spectra (4000–400 cm −1 ) of synthetic calcic amphiboles in the tremolite-pargasite series and of various natural calcic amphiboles have been investigated. The pargasite substitution, a combination of the Tschermak (= [4] Al [6] Al [6] Mg −1 [4] Si −1 ) and edenite (= [4] Al [A] Na [4] Si −1 [A] □ −1 ) substitutions, causes the following features in the region 1200–600 cm −1 . (1) Weak [4] Al-O stretching bands appear at 895 and 815 cm −1 that are distinct from the 955 and 925 cm −1 Si-O stretching bands in tremolite. (2) There is a reduction in the intensity and frequency of the Si-O-Si symmetric bending band (=“chain breathing” mode) at 750 cm −1 in tremolite, and there is an appearance of medium-strong composite bands having a weak shoulder on the high-frequency side near 690 cm −1 . These bands are assigned to Si-O-Al deformation bands. (3) Two OH-libration bands at 690 and 650 cm −1 become weak and broad composite bands from 720 to 610 cm −1 . And (4) because the intensity and frequency of the band at 640 cm −1 in tremolite is affected neither by deuteration nor by the pargasite substitution, this band is ascribed to O- [T2] Si-O bending. Even in pargasite, most T2 sites are occupied by Si, so that the O2- [T2] Si-O4 bending mode will be dominant in this amphibole. The same behavior occurs for the synthetic fluorogallian tremolite-pargasite series but with larger downward frequency shifts—Ga-O stretching bands appear at 880 and 780 cm −1 , and an Si-O-Ga bending band appears at 605 cm −1 . The major T-O-T and O-T-O deformation bands in synthetic amphiboles are readily apparent in natural calcic amphiboles whose compositions are near the tremolite-pargasite join.

http://www.minsocam.org/msa/ammin/toc/Abstracts/2008_Abstracts/July08_Abstracts/Ishida_p1112_08.pdf

Mid-IR bands of synthetic calcic amphiboles of tremolite-pargasite series and of natural calcic amphiboles

Infrared hydroxyl librational bands of talc-willemseite solid solutions (Mg–Ni talcs) have been explained by analogy with those of amphiboles. Two OH librational bands at 710 and 668 cm−1 appear in talc-willemseite solid solutions, because the degeneracy of a single OH librational vibration in talc and willemseite end-members is lifted by the substitutions of their octahedral cations. Comparison of infrared spectra of natural and hydrothermally deuterated A site-vacant and Al(IV) (tetrahedral Al)-free amphiboles reveals that two bands at 700 and 690–640 cm−1 are also ascribed to OH librations.

Identification of infrared OH librational bands of talc-willemseite solid solutions and Al(IV)-free amphiboles through deuteration

Vibrations involving hydroxyls in the infrared spectra of two synthetic 7 A trioctahedral minerals (amesite and aluminian lizardite) and of seven natural 14 A minerals (five trioctahedral chlorites of the Mg–Fe series, sudoite, and cookeite) have been investigated by comparison of the spectra with those of partially deuterated forms obtained by hydrothermal treatments with D2O. The results are interpreted to indicate that the OH bands between 850 cm−1 and 600 cm−1 in the trioctahedral minerals arise from librations of the outer OH in the 7 A minerals or the interlayer OH in the 14 A minerals, expressed by (SiAl)O–OH (∼800 cm−1) and (SiSi)O–OH (∼720 cm−1), and of the inner OH in the 7 A minerals or the 2 : 1 layer OH in the 14 A minerals (∼650 cm−1). These librations are correlated with the OH stretching vibrations in a reversed frequency relation. The shoulders around 930 cm−1 in sudoite and cookeite are confirmed to be due to the dioctahedral 2 : 1 OH. Some additional information on the OH stretching bands and on the lattice vibration bands has also been obtained.

Infrared study of some 7.ANGS. and 14.ANGS. layer silicates by deuteration.

High-resolution transmission-electron microscopy (HRTEM) and infrared spectroscopy (FTIR) analyses have been done on amphiboles near the join tremolite (Ca2Mg5Si8O22(OH)2 = TR)-pargasite (NaCa2Mg4Al3Si6O22(OH)2 = PG) in the ternary system tremolite-pargasite-cummingtonite (Mg7Si8O22(OH)2 = MC) that were synthesized previously by Sharma and Jenkins (1999). Represen- tative samples across the join were examined in detail by HRTEM to document the presence and concentration of chain multiplicity defects (CMFs). There was relatively little change in the defect density with composition, with the tremolitic sample (TREM 23-13) having the highest defect con- centration (6%) and the more PG-rich samples having slightly lower CMF concentrations (4-5%). CMFs with multiplicities of 1, 3, 4, 5, and 6 were observed, usually as isolated chains, with the most common being triple-chain slabs. Correction of the bulk composition of the tremolitic amphibole for the presence of these Mg-rich, wide-chain defects reduces the MC content from an apparent value of 8.5 to 4-7.5 mol% MC, depending on which composition is used for the triple-chain defect. The entire amphibole join was examined by FTIR spectroscopy in the OH-stretching region (3000-3800 cm -1 ) for the purpose of determining the presence of short-range order. A total of 10 component bands were fitted to the spectra across the join. These bands were assigned to specific cation con- figurations on the basis of earlier studies of the FTIR spectra of chemically simplified amphibole joins pertinent to this study. The extent of short-range order was qualitatively determined by com- paring the observed intensities for groups of related bands, corrected for differences in their molar absorptivities, to their calculated intensities based on random-mixing probabilities. From this exer- cise, it is observed that the intensities of sodic amphibole configurations are consistently high, tremolite is lowest near the middle of the join, and aluminous amphibole configurations cross over from being higher (at low Al contents) to being lower (at high Al contents) than expected near the middle of the join. These differences between observed and predicted band intensities may reflect the presence of deviations in the thermodynamic activities of amphibole components from those predicted on the basis of random-mixing models.

/pdf/infrared-and-tem-characterization-of-amphiboles-synthesized-5at0a41ye4.pdf

Infrared and TEM characterization of amphiboles synthesized near the tremolite-pargasite join in the ternary system tremolite-pargasite-cummingtonite

Fine structure in the principal OH-stretching bands of amphiboles of the tremolite-ferro-actinolite series have been examined. In samples with partly filled A sites, a broad (composite) band is observed at 3725∼3680 cm - 1 and is assigned to two types of configurations: (M1M1M3)-OH- A (Na,K): T 1 Si T 1 Al in which Al occurs at the T1 site, and (M1M1M3)-OH- A (Na,K)- O 3 (O 2 - ,F - ,Cl - ); the component of (M1M1M3)-OH- A (Na,K): T 1 Si T 1 Si configuration is small, because Na and K at the A site are locally associated with Al at an adjacent T1 site. In tremolite, manganoan tremolite, and Fe 2 + -poor actinolite, a weak shoulder on the principal A band at -3669 cm - 1 is assigned to the configuration M 4 Ca M 4 (Mg,Fe 2 + ,Mn 2 + ,Na):(MgMgMg)-OH- A □: T 1 Si T 1 Si (□ = vacancy). Fine structure in the principal bands B (B' and B") and C (C' and C") are also observed: the higher-frequency band B" is assigned to M 1 Fe 2 + M 1 Mg M 3 Mg-OH- A □, and the lower-frequency band B' to M 1 Mg M 1 Mg M 3 Fe 2 + -OH- A □; the higher-frequency band C' is assigned to M 1 Fe 2 + M 1 Fe 2 + M 3 Mg-OH- A □ and the lower-frequency band C" to M 1 Mg M 1 Fe 2 + M 3 Fe 2 + -OH- A □. Some broad OH-stretching bands attributed to (M1M1M3)-OH- A □: T 1 Si T 1 Al are observed at 3640∼3580 cm - 1 . In amphiboles of the tremolite-ferro-actinolite series that show a substantial B [(MgMgFe 2 + )-OH] band, a new OH-stretching band (at around 3641 cm - 1 ), E, appears near the principal C band (at around 3643 cm - 1 ) on heat treatment. The shape of band E is similar to that of the original band B, and its local configuration is O 2 - -(MgMgFe 3 + )-OH - . A weak and broad band A** appears at -3690 cm - 1 on heat treatment of some Na-bearing actinolites, and is ascribed to the (MgMgMg)-OH- A Na-O 2 configuration.

Kiyotaka Ishida

Papers

Mid-IR bands of synthetic calcic amphiboles of tremolite-pargasite series and of natural calcic amphiboles

Identification of infrared OH librational bands of talc-willemseite solid solutions and Al(IV)-free amphiboles through deuteration

Infrared study of some 7.ANGS. and 14.ANGS. layer silicates by deuteration.

Infrared and TEM characterization of amphiboles synthesized near the tremolite-pargasite join in the ternary system tremolite-pargasite-cummingtonite

Fine structure of infrared OH-stretching bands in natural and heat-treated amphiboles of the tremolite-ferro-actinolite series