Nanoparticles are ubiquitous in nature and are also found in raw coal, which plays an irreplaceable role in the global economy. In this study, raw coal samples were obtained from Gaojiapu Coal Mine in Shanxi Province, China. The elementary composition of nanoparticles was determined using energy-dispersive X-ray spectroscopy. The structural and chemical characteristics of nanoparticles were analyzed using transmission electron microscopy. Results revealed that there were multiple types of nanoparticles in the raw coal, such as S-, Ca-, Ba-, Ni-, Cr-, Si-, Sr-, and V-bearing nanoparticles. These nanoparticles exhibited various sizes and complex, irregular shapes. Our findings revealed that elemental nanoparticles occur in raw coal. These nanoparticles include celestite and barite nanoparticles. In addition, nanoparticles with Ni, Cr, and V in composition are also included in raw coal. These nanoparticles, which contain heavy metal elements, have great potential to harm the human body. Meanwhile, compared with the characteristics of nanoparticles produced by coal combustion, the nanoparticles in raw coal may be an important potential source of the nanoparticles produced by coal combustion.

Spinodal decomposition is an important mechanism of exsolution. However, spinodal decomposition has not been observed in natural sulfide intergrowths. We utilized focused ion beam (FIB) and transmission electron microscopy (TEM) techniques to confirm spinodal decomposition in natural sulfide intergrowths (chalcopyrite and bornite). According to FIB and TEM analyses, spinodal decomposition occurred as small and curving alternating dark and bright fluctuations in natural bornite–chalcopyrite intergrowths. Due to the low temperature that drove the exsolution mechanism, fluctuations ~10 nm wide and 20–200 nm long contained non-stoichiometric and tetragonal bornite and chalcopyrite. The corresponding electron diffraction of spinodal decomposition displayed a satellite spot in the [−210] direction for bornite, and the (200)* and (224)* of chalcopyrite paralleled the (24−2)* and (242)* of bornite, respectively. These observations all agreed with spinodal decomposition, two coexisting phases formed with a crystallographic orientation relationship, which indicated the first observation of spinodal decomposition in natural sulfide intergrowths. These findings confirmed that spinodal decomposition is a mechanism for natural crystal growth. As spinodal decomposition is larger in extent and faster than nucleation and growth, other Cu ore deposits may also form via this mechanism.