ANALYSIS AND IDENTIFICATION OF INCLUSIONS IN TYPE IIA PINK DIAMONDS

Diamonds, and their associated inclusions, can provide a window into the lithospheric and sub-lithospheric mantle below us. Diamonds transported to the surface can provide minerals that can help us understand the composition of the deep mantle and processes occurring within it. While previous researchers have investigated inclusions in colorless and pink type Ia diamonds (Kaminsky et al., 2000), there have been no systematic inclusion analysis and identification studies conducted specifically on pink type lla diamonds. Preliminary observations show sub-lithospheric inclusions from a small number of pink type IIa diamonds (Smith et al. 2016). The purpose of this examination was to target pink type IIa diamonds and further explore the range of inclusions they contain.

A suite of 30 pink type IIa diamonds containing inclusions were studied using Raman spectroscopy. All type IIa diamonds studied exhibited the 550 nm absorption band in its Vis-NIR absorption spectrum which causes a pink coloration in diamond. The inclusions identified within 30 type lla pink diamonds were mainly sub-lithospheric origin inclusions such as breyite, larnite, and coesite. There was also a lesser amount of lithospheric inclusions such as forsteritic olivine, enstatite, and garnet.

The presence of these inclusions within the type lla pink diamonds suggests that they predominately came from the sub-lithospheric mantle at depths ranging from 360 to 750 km. While the identification of these inclusions may be obtainable, the cause of the pink color in these diamonds is more difficult. The color may be attributed to plastic deformation within the mantle, but additional research on the subject needs to be conducted.

The examined inclusions suggest that the majority of pink type IIa diamonds are sub-lithospheric in origin, which is consistent with previous findings from studies of type IIa diamonds in general irrespective of color and that super deep gem diamonds may be more common than previously thought.

REFERENCES

Kaminsky, F.V., et al. (2000) Diamond from the Guaniamo Area, Venezuela. Canadian Mineralogist, 38, 1347–1370.

Smith, E. M., et al. (2016) Large gem diamonds from metallic liquid in Earth’s deep mantle. Science, 354(6318), 1403-1405.