<p>Agate pebble samples were collected at the Tevinskoye deposit (northern Kamchatka Peninsula, Russia). Simple organic radicals trapped in the microcrystalline portions of the sample, consisting predominantly of chalcedony, were studied using EPR spectroscopy. Traces of fossilized carbonaceous matter were discovered in agate for the first time. Due to the free rotation of the radicals in untreated samples, only isotropic EPR spectra associated with ĊH₃, R1 ĊH₂, R2 ĊH₂, and CO₂⁻ were observed. The EPR spectra changed upon grinding or heating of the agate samples. The carbon radical Ċ, localized in complex organic molecules, was detected after stepwise annealing of the samples at temperatures above 300&#xa0;°C. Changes in the <i>g</i>-factor, linewidth, and resonance line shapes of the carbon radical depending on the annealing temperature were investigated and discussed.</p>