Blue-fluorescing amber from Cenozoic lignite, eastern Sikhote-Alin, Far East Russia: Preliminary results

•Multi-colored amber was subjected to FTIR, SEM-EDA, and fluorescence measurements.•The blue amber variety contains CO2, OH and possibly CH groups.•Wildfire heating and cooling in water might cause the extreme amber polymerization.•Fluorescence measurements suggest that the blue amber glow is caused by perylene.

Blue and greenish-yellow, in addition to ordinary yellow-orange amber, has recently been found in a lignite seam in the Zerkal'nenskaya depression, Primorsky Krai, Russia. The amber is associated with abundant charcoal and fusain fragments in the host rocks. Its FTIR spectra indicate the presence of significant quantities of volatile matter, including free hydroxyl groups and carbon dioxide. Both CO2 and OH− contents are greater in the greenish-yellow and blue hard varieties, suggesting rapid heating, possibly from a wildfire, followed by rapid cooling in water as a causative agent of amber hardening and extreme polymerization. This process and the following amber deposition in the reduced environment might produce the fluorescent aromatics that have been previously suggested and confirmed by this study as the blue glow main cause.