Nano and sub-micro inclusions as probes into the origin and history of natural diamonds

a r t i c l e i n f o Keywords: Diamond Raman spectroscopy EDAX Inclusion Platinum group element Kimberlite Five natural faceted diamond samples, considered to have inherent submicroscopic and nanometric inclusions, were studied using various techniques such as Raman spectroscopy, Raman microscopy, scanning electron microscopy (SEM), and energy dispersive analysis of X-rays (EDAX). The principal focus was to find out the chemical nature of the inclusions and their distribution. As a confirmative tool, laser desorption ionization mass spectrometry (LDI MS) was used for the characterization of the inclusions. Our study suggests that the inclusions in diamond belong to the pyroxene group of silicate minerals with Fe, Mg, Ca, Ru, and Cr as the major elements. As evidenced by the absence of alkali, aluminum, and rare earth elements in the inclusion, the diamond can be of peridotitic origin. Interestingly, we found that chromium scavenges Ru, a platinum group element (PGE), and other metals such as Nb, Co, and Ni, entrained into the pyroxene inclusions. We established that the diamond sample in which inclusions are found is of Kimberlitic origin. Among various gem stones, diamond is considered as the prince of solids, since it is relatively inert, unreactive and hard. Due to this reason, its formation, genetic history and environment at which it formed have been looked at in great detail. Since purest diamonds, free from any inclusions, do not shed any light on their history, the studies of primary mineral inclusions [1] such as those crystallized and encapsulated during (syngenetic) or before (protogenetic) the growth of the gems throw light on their genesis as well as its physical and chemical history. These mineral inclusions are important indicative sources of information on the composition of continental lithospheric mantle at depths exceeding 120–150 km and deeper, from where the genesis of diamond is now traced [2]. They also point out a vital knowledge of the mass balance and depth dependant distribution of certain elements such as carbon and sulfur. The existence of metals like Au, Pt, Pd, etc., as inclusions in diamond can give an idea about the potential areas and deposits of such elements, and may have important implications to the mining industry. The host rocks of diamonds have been investigated extensively over the past few decades in search of their origin and genesis [3]. Formation of diamond occurs in the interior of Earth from the peridotite or eclogite …