Lab Notes Gems & Gemology, Spring 2015, Vol. 51, No. 1

Diamond in Diamond

Diamond within black diamond
Figure 1. This 1.69 ct Fancy black round brilliant diamond contained an octahedral diamond crystal. Photo by Jian Xin (Jae) Liao.
The New York laboratory recently examined a 1.69 ct Fancy black round brilliant diamond (figure 1). The type Ia diamond contained an abundance of tiny cloud inclusions and strong hydrogen-related absorptions, both common features for this type of diamond. We observed numerous etch channels with brown radiation staining, also normal features for diamonds of this type and color. But we also observed a sizable octahedral crystal inclusion that broke the surface of a pavilion facet (figure 2, left). The surface-breaking area was approximately 150 × 250 microns according to the Raman microscopic image. The actual dimensions of the entire included crystal could not be determined.

Diamond within diamond photomicrographs
Figure 2. Left: This photomicrograph reveals natural etch channels with brown radiation staining, as well as an octahedral crystal inclusion (the inset shows the surface-breaking outline). Center: The Raman map of the 1332 cm–1 FWHM clearly outlines the surface break of the octahedral diamond inclusion. The inset in the left-side image represents the Raman mapping area. The image was taken in a grid pattern measuring FWHM of the diamond Raman peak at 1332 cm–1. More than 300 Raman spectra collected at multiple points on the grid were translated into this map by the software. Each colored pixel represents the FWHM value, and similar FWHM values will be shown in similar colors. Noticeably different colors outlining the inclusion indicate that it is not part of the host diamond and that it formed in a different geological environment. Right: DiamondView imaging shows that the diamond inclusion was captured during the second phase of growth. Photomicrographs by Paul Johnson (left and right) and Kyaw Soe Moe (center).
The exposed crystal inclusion had the morphology of a natural diamond crystal, and Raman analysis easily identified it as diamond. Both the host diamond and inclusion show sharp 1332 cm–1 Raman bands, indicating high crystallinity. The graphite peak at approximately 1580 cm–1 was not observed in either. Raman mapping showed that the full width at half-maximum (FWHM) of the inclusion’s 1332 cm–1 peak was different from that of the host diamond (figure 2, center). In the map, each colored pixel represents the FWHM value of the 1332 cm–1 Raman peak. The colored pixels of the inclusion were decidedly different from those of the host diamond, confirming that it formed in a different geological environment. We also observed differences between the photoluminescence (PL) spectra of the inclusion and the host diamond, evidence that the diamond inclusion formed in a different environment and was later incorporated as a protogenetic inclusion. This also suggests that this diamond may have traveled from its original formation environment to another geological environment after crystallization.

A DiamondView image shows the diamond crystal to have been captured in a second growth phase of the host diamond crystal (figure 2, right). This is the first documented case of a diamond crystal inclusion with a different origin than that of the host diamond.

Paul Johnson and Kyaw Soe Moe are researchers at GIA’s New York laboratory.