Please use this identifier to cite or link to this item: https://hdl.handle.net/2440/130791
Citations
Scopus Web of Science® Altmetric
?
?
Type: Journal article
Title: Silicon-oxygen region infrared and raman analysis of opals: the effect of sample preparation and measurement type
Author: Curtis, N.J.
Gascooke, J.R.
Pring, A.
Citation: Minerals, 2021; 11(2):173-1-173-31
Publisher: MDPI AG
Issue Date: 2021
ISSN: 2075-163X
2075-163X
Statement of
Responsibility: 
Neville J. Curtis, Jason R. Gascooke and Allan Pring
Abstract: An extensive infrared (IR) spectroscopy study using transmission, specular and diffuse reflectance, and attenuated total reflection (ATR) was undertaken to characterise opal-AG, opal-AN (hyalite), opal-CT and opal-C, focussing on the Si-O fingerprint region (200–1600 cm−1). We show that IR spectroscopy is a viable alternative to X-ray powder diffraction (XRD) as a primary means of classification of opals even when minor levels of impurities are present. Variable angle specular reflectance spectroscopy shows that the three major IR bands of opal are split into transverse optical (TO) and longitudinal optical (LO) components. Previously observed variability in powder ATR is probably linked to the very high refractive index of opals at infrared wavelengths, rather than heterogeneity or particle size effects. An alternative use of ATR using unpowdered samples provides a potential means of non-destructive delineation of play of colour opals into opal-AG or opal-CT gems. We find that there are no special structural features in the infrared spectrum that differentiate opal from silica glasses. Evidence is presented that suggests silanol environments may be responsible for the structural differences between opal-AG, opal-AN and other forms of opaline silica. Complementary studies with Raman spectroscopy, XRD and scanning electron microscopy (SEM) provide evidence of structural trends within the opal-CT type.
Keywords: opal; hyalite; geyserite; menilite; infrared; Raman; X-ray diffraction; scanning electron microscopy; gem; silica
Rights: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).
DOI: 10.3390/min11020173
Grant ID: http://purl.org/au-research/grants/arc/LE190100161
Appears in Collections:Aurora harvest 4
Physics publications

Files in This Item:
File Description SizeFormat 
hdl_130791.pdf20.61 MBAdobe PDFView/Open


Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.