Raman Identification of Inclusions in Diamond

Abstract

Diamonds and their inclusions are some of the most scientifically valuable samples of the Earth (Haggerty 1999; Shirey et al. 2019). Among the analytical techniques used to study diamonds, Raman spectroscopy offers several advantages that make it an appealing tool for characterizing inclusions. It is a relatively low-cost, rapid, and non-destructive option, requiring minimal sample preparation, if any. Inclusions can often be characterized in-situ, while still fully enclosed in their diamond host, which ensures that no material is inadvertently lost (e.g., fluid) and the remnant pressure of the inclusion–host system is preserved. The pressure within inclusions can be on the order of several gigapascals (e.g., Nasdala et al. 2003) and is especially important for stabilizing the crystal structure of certain highpressure minerals, such as ringwoodite, in sublithospheric diamonds (Pearson et al. 2014). Ideally, Raman spectroscopy can be complemented by other in-situ methods, such as infrared spectroscopy (FTIR), micro-beam X-ray diffraction (XRD), X-ray computed tomography (CT), and synchrotron X-ray fluorescence (XRF). Raman spectroscopy can serve as a first step to help characterize inclusions before employing more time-consuming or destructive analytical techniques, but it can also serve as a powerful tool in its own right for diamond research (e.g., Liu et al. 1990; Gillet et al. 2002; Nasdala et al. 2003, 2005; Brenker et al. 2005; Walter et al. 2011; Howell et al. 2012; Pearson et al. 2014; Nimis et al. 2016; Smit et al. 2016; Smith et al. 2016b, 2018; Anzolini et al. 2018; Kemppinen et al. 2018). This chapter is the first Raman spectroscopy review specifically applied to inclusions in diamond.