Gemmological and Spectral Characteristics of Amber from Ethiopia

Specimens of greenish-yellow amber from Ethiopia were collected and tested for their gemmological and spectroscopic characteristics. The test results showed that amber from Ethiopia has a refractive index of 1.54-1.55(point measurement) and a density of 1.022~1.058 g/cm³. Wave-like anomalous extinction was visible under crossed polarizer. The amber matrix showed a strong blue fluorescence under long-wave ultraviolet light, while after a long period of natural oxidation in the air, the fluorescence turned to blue-green with a slightly lower intensity.The maroon oxidized surface showed a green fluorescence in medium intensity. In the transitional zone from the oxidized surface to the inner matrix, the body colour showed gradient transition from brownish red to yellow, however the long-wave ultraviolet fluorescence image showed a clear boundary of the transitional zone. Observed by microscope, the amber contained inclusions such as gas-liquid two-phase inclusions, gas bubbles, black flocs, "samara-like" inclusions, and lamellar or wave-like patterns caused by multiple stages of resin accumulation. Both IR and Raman spectra showed a combination of aliphatic and C=O functional groups typical of amber, with small amount of unsaturated components.The vibration spectral characteristics were similar to those of fossilized resins from Leguminosae plants. The value of I_{1 650 cm^-1/1 442 cm^-1} in the Raman spectra indicating the maturity of amber fell in the range of 0.69-0.75, which was rather close to that of amber from Dominica. The UV-Vis-NIR spectra of greenish-yellow amber from Ethiopia showed a broad band centered at 630 nm, causing the unique greenish tint of its body colour.