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

Content Provider	Semantic Scholar
Author	Ishida, Kiyotaka Jenkins, David M. Hawthorne, F. C.
Copyright Year	2008
Abstract	Abstract 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 fluoro-gallian 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.
Starting Page	1112
Ending Page	1118
Page Count	7
File Format	PDF HTM / HTML
DOI	10.2138/am.2008.2756
Volume Number	93
Alternate Webpage(s)	http://www.minsocam.org/msa/ammin/toc/Abstracts/2008_Abstracts/July08_Abstracts/Ishida_p1112_08.pdf
Alternate Webpage(s)	https://doi.org/10.2138/am.2008.2756
Language	English
Access Restriction	Open
Content Type	Text
Resource Type	Article