Striking differences in potentiality of diamond mineralization are shown in the three kimberlite belts of Changmazhuang, Xiyu and Poli in Mengyin, Shandong Province. Previous studies of diamonds have focused on the Changmazhuang belt; however, genesis of diamonds from the other two belts, as well as comparative studies on diamonds from the three belts, are relatively scarce. In this paper, the morphological and spectral features of 44 diamonds ranging from 0.03 mg to 16.46 mg in weight from the three belts are investigated systematically by microscopic observation, Fourier-transform infrared spectroscopy (FTIR) and Raman spectroscopy. The results show that the formation temperature is 1118–1251 °C for Changmazhuang diamonds, 1091–1167 °C for Xiyu diamonds, and 1132–1172 °C for Poli diamonds. Diamonds in the three belts exhibit uniform pre–kimberlite surface features of multiple serrate, triangular laminae and small trigons, suggesting a similar condition of diamond destructive metasomatism caused by carbonatitic and silicate-carbonatitic melts. However, Poli diamonds probably suffered from a silicate component-enriched carbonatitic melt in the deep mantle. Nitrogen contents (0–539 ppm) of diamonds from the three belts have a slight impact on their morphological features.

A total of 48 natural alluvial diamonds from the Yangtze Craton, China, also called Hunan diamonds, were studied using morphology and IR spectroscopy. These diamond samples, collected downstream of the Yuan River, Hunan Province, with unknown host-rock source(s), were observed by scanning electron microscope (SEM) and Fourier-transform infrared spectroscopy (FTIR). Most Hunan diamonds are monocrystal forms of octahedra, tetrahexahedra (THH) and dodecahedra; octahedral–rhom-dodecahedral transitional behaviors and irregular forms are also visible. Trigons and tetragons, terraces and shield-shaped laminae are surface features that frequently indicate dissolution and reabsorption; green and brown spots, network patterns, and other mechanical abrasion marks are typical evidence of long-time deposition and transportation of Hunan diamonds. The main types of Hunan diamonds are type IaAB and type Ⅱa. Diamond samples have a wide range of total nitrogen content (N_tot) from 196–1094 ppm. Two populations are distinguished by two-peak distribution models of N_A (A-center concentrations) and %B (proportion of aggregated nitrogen). Hunan diamonds are low in structure hydrogen (0.03–4.67 cm⁻¹, mostly below 1 cm⁻¹) and platelets (0.23–17 cm⁻¹, mostly below 2 cm⁻¹). Moreover, there is a significant positive correlation between the hydrogen correlation peak and N_tot, which is similar to Argyle diamonds. The temperature conditions of the diamond formation have been estimated at 1075–1180 °C, mainly conforming to the kimberlite diamond range. Besides, some samples with slightly higher temperatures are close to the ultramafic-related Juina diamonds. Therefore, the FTIR characteristics analysis and comparison indicate the multiple sources of Hunan diamonds.

The ultra-deep genesis of ophiolitic peridotite has reshaped our perception of the genesis of the oceanic mantle. Although ultra-high pressure (UHP) mineral assemblages have been unearthed in dozens of ophiolites in different orogenic belts around the world, the vast majority of them have been limited to podiform chromitites formed in suprasubduction zone (SSZ) settings, leaving uncertainty about whether such UHP minerals are intrinsic to the oceanic mantle or influenced by a specific mantle rock type. Here, we report on the occurrence of diamonds recovered from the harzburgites within the Skenderbeu massif, Mirdita ophiolite. The whole-rock, mineralogical major and trace element compositions, and redox states of the harzburgites align with modern abyssal harzburgites. Trace element modeling of clinopyroxene indicates that harzburgites have endured varying degrees of garnet-facies melting (~2%–5%) before progressing to spinel-facies melting (~10%–12%). Mineralogical characteristics further support that the Skenderbeu harzburgites underwent late-period MORB-like melt metasomatism in a forearc spreading center. An unusual mineral assemblage of diamonds has been separated from the studied harzburgites. The first occurrence of ophiolite-hosted diamonds discovered in the forearc harzburgites, together with previous similar discoveries in the SSZ ophiolitic chromitites, suggest that the ophiolite-hosted diamonds are not specific to certain mantle rocks.