Welcome in the mines of ancient ETHIOPIA
(Note that these mines are now in Eritrea, which won its independence in 1993)
Emeralds from ancient Ethiopia were known to the Mediterranean civilizations, but the location of the mines was lost for centuries. It is likely that they came from the granititic pegmatites found SE of Massua (Massawa) in Eritrea, a modern source of emeralds.
For each mine we calculated the medium value of lattice parameter.
For each mine we calculated the medium value of chemical analyses (analysed 20 point ) by EMPA (Cameca CX 827).
Mn, Se, F, Rb are under detection limits except in few cases. Li and Be are not determined.
Chemical analyses have been normalized at 85%.
H2O was deetermined by EA 1108 Carlo Erba ( gas cromatographer).
Reflectance FTIR (Fourier Transform Infrared Spectra) of gemstones have been acquired using a microscope IRscopeII (Bruker) accumulating 200 scans with a resolution of a cm-1 or better, in the range 7000-600 cm-1. Here are given only the skeletal bands which lie in the interval 1500-600 cm-1 When the samples were suitably cut in direction parallel or normal to the c axis, polarized spectra were also obtained on the pinacoid or on the basis respectively or both. According to the group theory 6A2u + 16 E1u infrared modes are predicted: the E1u modes are observed in the spectrum when the electric field is perpendicular to the c-axis (ordinary ray) and the A2u modes are observed for the extraordinary ray (E|| c). Therefore, non degenerate bands (A2u) are observed on pinacoids and show intensity changes in polarization, while degenerate bands (E1u) are detected on basis spectra and show only a lowering in intensity in polarized light.
1. Sinkankas J. 1981 "Emeralds and Other Beryls" Pensylvania, Chilton Book Co. p. 542-548