2024

Nickel-bearing type IA natural colourless diamond

By Dr. M. Mintrone, first published in Facette 29 (May 2024)

In gemmology, nickel is generally associated with synthetic HPHT diamonds through the presence of the well-known nickel-related (Ni-related) centre at 883/885 nm, which is rarely present in natural diamonds. However, many studies reported the presence of other Ni- related centres in yellow, grey, and pink diamonds, suggesting that nickel in natural diamonds could be more frequent than previously thought (e.g. Chalain 2003; Gaillou et al., 2010: Breeding et al., 2020).
Figure 1: Fluorescence of the studied natural colourless diamonds observed under UV excitation (365 nm). Note that this fluorescence is typical of natural colourless diamonds. Figure: SSEF.
In this study, we investigated the presence of nickel-related centres in natural colourless diamonds (Figure 1). We first analysed 8000 natural diamonds with photoluminescence (PL) at room temperature, followed by PL at liquid nitrogen temperature (-196°C) on 50 representative diamonds. Our preliminary results with room temperature PL show that Ni-related centres between 700 -800 nm are present in ca. 40% of the analysed diamonds, as confirmed by low-temperature PL (Figure 2). Infrared spectroscopy revealed that all those diamonds are type Ia.
Figure 2: Representative spectra of natural colourless diamonds were collected at liquid nitrogen temperature with a 633 nm laser. The spectra are vertically shifted for clarity. Figure: SSEF.
The 883/885 nm centre is related to a nickel-vacancy defect, commonly detected in HPHT synthetic type Ib, IIa, and IIb diamonds and some natural type IIa diamonds. Conversely, the nickel-related centres detected in our natural colourless type Ia diamonds are thought to be linked with the aggregation of nickel and nitrogen defects, which takes place over geological timescales. To summarize, our study confirms that nickel is a common impurity of natural colourless diamonds. Moreover, nickel in diamonds is present in many different forms and as shown its presence does not necessarily identify such a stone as a synthetic HPHT diamond.

References

Chalain, J-P. 2003. A natural yellow diamond with nickel-related optical centers. Gems & Gemology, 39, 325-326.
Gaillou, E., Post, J.E., Bassim, N.D., Zaitsev, A.M., Rose, T., Fries,
M., Stroud, R.M., Steele, A., Butler, J.E. 2010. Spectroscopic and microscopic characterization of color lamellae in natural pink diamonds. Diamond and Related Materials, 19, 1207-1220.
Breeding, C.M., Eaton-Magaña, S., Shigley, J.E., 2020. Naturally colored yellow and orange gem diamonds: the nitrogen factor. Gems & Gemology, 56(2), 194-219. http://dx.doi.org/10.5741/GEMS.56.2.194.