A: Variation in shape and appearance of the collected amber grains; B–E: views of amber grains under SEM; F–K: close-up views of amber grain thin sections under optical microscope. In details: B: section of translucent grain in the form of an elongated drop-shaped; C: part of elongated drop-shaped grain with surface cracks and peripheral partial colonization by filamentous micro-organisms; D: uniformly opaque grain; E: heterogeneous opaque grain with bubbles; F: translucent grain with orange outline; G: partially colonised translucent grain by a filamentous network (black arrow); H: opaque grain entirely colonised by a filamentous network; I–J: heterogeneous opaque grains with centripetal colonization areas by micro-organisms; K: heterogeneous opaque grain with dense bubbles.