Gemmological and Spectroscopic Characteristics of Different Varieties of Amber from the Hukawng Valley, Myanmar

With its broad range of varieties, Burmese amber may show various optical effects, including 'oil gloss' (a red or green surface fluorescence effect) and phosphorescence phenomena. Samples representing golden, brown, red ('blood'), 'beeswax' and 'root' ambers were characterised, as well as those showing red or green 'oil gloss'; many of these also displayed phosphorescence. Common internal features seen with optical microscopy include reddish brown dot-like inclusions in brown amber and flow-banded concentrations of bubbles in 'beeswax' and 'root' ambers (the latter displaying patterns comprised of opaque light- and dark-coloured layers). SEM imagery revealed various scaly or layered structures on freshly broken surfaces, micro-bubbles in some samples and distinctive hollow micro-channels in 'root' amber. Fluorescence spectra recorded luminescence centres at 432 and 470 nm in all samples, and additionally at 650 nm (+/- 625 nm) in red 'oil gloss' amber. The 'oil gloss' appearance is caused by a mixture of surface fluorescence and the amber's body colour. Phosphorescence spectroscopy showed that the effect was strongest at 525 nm, and the phosphorescence lifetime measured at this emission wavelength ranged from 0.134 to 1.396 seconds. (C) 2020 Gem-A (The Gemmological Association of Great Britain)