Origin of milky optical features in type IaB diamonds: Dislocations, nano-inclusions, and polycrystalline diamond

Natural-Color Fancy White and Fancy Black Diamonds: Where Color and Clarity Converge

“…In contrast with the observations of "hazy" diamonds, in the diamonds that appeared "cloudy" instead, Gu et al (2019) detected nano-inclusions (described as negative crystals) containing solid nitrogen. As with prior researchers, they confirmed the size ranges of these features as ~20 to 200 nm.…”

“…Gemologists, however, often describe them as "hazy," "milky," or "cloudy" when observing them through a microscope (figure 4). Recent studies on both hazy and cloudy diamonds show that these observations (e.g., Rudloff-Grund et al, 2016;Kagi et al, 2016;Gu et al, 2019) are due to two distinct phenomena: nano-inclusions and dislocation loops, both described below. These studies have shed light on the nature of these features, which can appear nondescript even at high magnifications with an optical microscope.…”

“…In comparison, inclusions that are large enough to be classified as crystals are generally larger than ~50 μm (500 times larger). The nano-inclusions appeared as octahedrons or elongated trapezoids, and were found to contain nitrogen; other researchers have confirmed the presence of nitrogen, but there is still no consensus on the exact configuration of the nitrogen (Kagi et al, 2016;Rudloff-Grund et al, 2016;Navon et al, 2017;Gu et al, 2019). Rudloff-Grund et al also found that areas of the diamond with these nano-inclusions correlated with detection of higher nitrogen and hydrogen by IR absorption mapping.…”

“…These studies have shed light on the nature of these features, which can appear nondescript even at high magnifications with an optical microscope. These features are best imaged and identified using more advanced forms of microscopy such as transmission electron microscopy (Rudloff-Grund et al, 2016;Gu et al, 2019). In TEM, a beam of elec-trons is transmitted through the sample to form an image.…”

“…Other researchers (Kagi et al, 2016) additionally found several transition metals (such as Ni) within these nano-inclusions. Gu et al (2019) continued this study by creating TEM foils with diamond that they deemed as only "hazy" or only "cloudy" based on their microscopic differences. They wished to see if distinguishing phenomena could be observed between the "hazy" and "cloudy" descriptions.…”