  The curious occurrence of perfectly spherical particles when a steel
substrate is slid against a hard abrasive was first observed and documented by
Robert Hooke in the 17$^{th}$ century. Similar particles have subsequently been
observed in numerous other abrasion-type processes, ranging from grinding of
steels to sliding rock faults. The prevalent hypothesis, originally proposed by
Hooke, is that these particles are formed due to high local temperatures
between the abrasive and the substrate, resulting in melting, droplet ejection
and subsequent resolidification -- the melting-resolidification hypothesis. In
this work, we revisit this phenomenon using \emph{in situ} analysis of a model
steel-abrasive contact geometry, complemented by analytical calculations. It is
found that the temperature within the contact zone, for typical contact
conditions used, is far from the melting point and that spherical particles do
not form in the absence of oxygen. We thereby propose a modification of the
melting-resolidification hypothesis, involving an intermediate exothermic
oxidation stage, and provide quantitative evidence for each step of the
process. Our results have implications for a wide class of abrasive systems
that involve the formation and utilization of spherical metallic particles
