Quantifying strain birefringence halos around inclusions in diamond
- Author(s)
- Dan Howell, Ian G. Wood, David P. Dobson, Adrian P. Jones, Lutz Nasdala, Jeff W. Harris
- Abstract
The pressure and temp. conditions of formation of natural diamond can be estd. by measuring the residual stress that an inclusion remains under within a diamond. Raman spectroscopy has been the most commonly used technique for detg. this stress by utilizing pressure-sensitive peak shifts in the Raman spectrum of both the inclusion and the diamond host. Here, we present a new approach to measure the residual stress using quant. anal. of the birefringence induced in the diamond. As the anal. of stress-induced birefringence is very different from that of normal birefringence, an anal. model is developed that relates the spherical inclusion size, R i, host diamond thickness, L, and measured value of birefringence at the edge of the inclusion, , to the peak value of birefringence that has been encountered; to first order . From this birefringence, the remnant pressure (P i) can be calcd. using the photoelastic relationship , where q iso is a piezo-optical coeff., which can be assumed to be independent of crystallog. orientation, and n is the refractive index of the diamond. This model has been used in combination with quant. birefringence anal. with a MetriPol system and compared to the results from both Raman point and 2D mapping anal. for a garnet inclusion in a diamond from the Udachnaya mine (Russia) and coesite inclusions in a diamond from the Finsch mine (South Africa). The birefringence model and anal. gave a remnant pressure of 0.53 - 0.01 GPa for the garnet inclusion, from which a source pressure was calcd. as 5.7 GPa at 1,175°C (temp. obtained from IR anal. of the diamond host). The Raman techniques could not be applied quant. to this sample to support the birefringence model; they were, however, applied to the largest coesite inclusion in the Finsch sample. The remnant pressure values obtained were 2.5 - 0.1 GPa (birefringence), 2.5 - 0.3 GPa (2D Raman map), and 2.5-2.6 GPa (Raman point anal. from all four inclusions). However, although the remnant pressures from the three methods were self-consistent, they led to anomalously low source pressure of 2.9 GPa at 1,150°C (temp. obtained from IR anal.) raising serious concerns about the use of the coesite-in-diamond geobarometer.
- Organisation(s)
- Department of Mineralogy and Crystallography
- External organisation(s)
- University College London, University of Glasgow
- Journal
- Contributions to Mineralogy and Petrology
- Volume
- 160
- Pages
- 705-717
- No. of pages
- 13
- ISSN
- 0010-7999
- DOI
- https://doi.org/10.1007/s00410-010-0503-5
- Publication date
- 2010
- Peer reviewed
- Yes
- Austrian Fields of Science 2012
- 1030 Physics, Astronomy, 105116 Mineralogy
- Portal url
- https://ucrisportal.univie.ac.at/en/publications/7927aed6-86fd-430b-9c24-17970bb38eaf