Beyond its renowned gemological value, diamond serves as a vital economic mineral and a unique messenger from Earth’s deep interior, preserving invaluable geological information. Since the Mengyin region is the source of China’s greatest diamond deposits, research on the diamonds there not only adds to our understanding of their origins but also offers an essential glimpse into the development of the North China Craton’s mantle lithosphere. In this article, 50 diamond samples from Mengyin were investigated using gemological microscopy, Fourier-transform infrared (FTIR) spectroscopy, Raman spectroscopy, DiamondView™, and X-ray micro-computed tomography (CT) scanning technologies. The types of Mengyin diamonds are mainly Type IaAB, Type IaB, and Type IIa, and the impurity elements are N and H. Inclusions in diamonds serve as direct indicators of mantle-derived components, providing crucial constraints on the pressure–temperature (P–T) conditions during their crystallization. Mengyin diamonds have both eclogite-type and peridotite-type inclusions. It formed at depths ranging from 147 to 176 km, which corresponds to source pressures of approximately 4.45–5.35 GPa, as determined by the Raman shifts of olivine inclusions. The discovery of coesite provides key mineralogical evidence for subduction of an ancient oceanic plate in the source region. The surface morphology of diamonds varies when they are reabsorbed by melts from the mantle, reflecting distinctive features that record subsequent geological events. Distinctive surface features observed on Mengyin diamonds include fusion pits, tile-like etch patterns, and growth steps. Specifically, regular flat-bottomed negative trigons are mainly formed during diamond resorption in kimberlite melts with a low CO₂ (X_CO2 < ~0.5) and high H₂O content. The samples exhibit varying fluorescence under DiamondView™, displaying blue, green, and a combination of blue and green colors. This diversity indicates that the diamonds have undergone a complex process of non-uniform growth. The nitrogen content of the melt composition also varies significantly throughout the different growth stages. The N3 center is responsible for the blue fluorescence, suggesting that it originated in a long-term, hot, high-nitrogen craton, and the varied ring band structure reveals localized, episodic environmental variations. Radiation and medium-temperature annealing produce H3 centers, which depict stagnation throughout the ascent of kimberlite magma and are responsible for the green fluorescence.

“Trapiche-like” texture is distinct from “trapiche” texture as typically observed in emeralds, amethysts, and aquamarines. It is also occasionally encountered in sapphires from Changle, eastern North China Craton. The advent of the trapiche-like texture has enhanced the ornamental value of sapphire, although its origin is still unclear. In this study, techniques, such as Fourier transform infrared (FTIR) spectroscopy, ultraviolet–visible (UV-Vis) spectroscopy, Raman spectroscopy, electron probe microanalysis (EPMA), and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), have been applied to test the spectroscopic data of the cores, arms, and blue sectors of trapiche-like sapphires from Changle and explore the mineralogical characteristics of different domains. The main component of the core, arms, and blue sectors of trapiche-like sapphire is corundum (Al₂O₃), with trace elements including Fe, Ti, Mg, Cr, V, Ga, etc. From arms to cores to sectors, trace elements show a trend of increasing and then decreasing. Nb and Ta elements are more enriched in the arms than in the sectors, indicating the existence of rutile. With changes in physicochemical conditions during magma evolution, rutile melted, and related voids were filled with glassy inclusions, which formed the arms of trapiche-like sapphires. Field observations of primary deposits, as well as petrological and geochemical analyses, reveal that the trapiche-like sapphire of Changle belongs to magmatic sapphire.