Abstract Natural microspherules are important tracers of geologic and environmental processes in modern and ancient deposits. However, anthropogenic contamination can dilute natural collections by releasing synthetic microspherules into the environment. We report on a collection of microspherules from Pikes Peak, a granitic batholith mountain in Colorado, USA. Most particles are smooth, glassy spheres and are compositionally homogeneous, while some particles do not indicate formation via a molten or vapor phase and are interpreted as erosional products. The glassy microspherules are compared to spheres found in road paint from London, United Kingdom, and show strong textural and compositional similarities. In particular, Na content is high, which is unexpected in natural spherules. The Pikes Peak spherules are interpreted as microspherules eroded from road markings, illustrating local contamination on the summit. In addition, two microspherules with potential natural origins were found. We propose criteria for distinguishing paint microspherules from their natural counterparts, which is vital when investigating ancient spherule‐forming processes as well as the impact of human activity on the environment. Quantifying the mass of microspherules found indicates high erosion rates of road paint, leading to microspherule abundances that could dominate the local microspherule flux.
Boyd et al. (Sun,) studied this question.