gems, inclusions, beryl, emerald, Madagascar

Emeralds from the Morafeno mining region near Mananjary, Madagascar, are characterized through measurements of physical properties, electron-microprobe analyses, polarized absorption spectroscopy, and microscopic examination of inclusions. The study places these commercially exploited mica-schist-hosted deposits within the history of Malagasy beryl discoveries and distinguishes true emerald from earlier reports of iron-coloured green beryl. Morafeno produces partly transparent emerald crystals several centimetres in size embedded in dark mica. Measured extraordinary refractive indices range from 1.580 to 1.582 and ordinary indices from 1.588 to 1.591, with birefringence of 0.008–0.009 and densities of 2.68–2.71 g/cm³. These properties broadly agree with earlier Malagasy data and overlap the lower range reported for Zambian emeralds, whose colour is also comparable. Analyses of six emeralds reveal medium to high magnesium and sodium concentrations, with 1.71–3.00 wt% MgO and 1.28–2.16 wt% Na₂O, together with 0.08–0.34 wt% Cr₂O₃ and 0.91–1.30 wt% total iron expressed as FeO. Element-correlation diagrams compare the samples with emeralds from other African deposits, Brazil, Australia, and Norway. Decreasing aluminium with increasing magnesium, accompanied by increasing sodium, is explained by magnesium substitution for aluminium and charge compensation by sodium occupying channels in the beryl structure. Visible and near-infrared spectra combine chromium-related emerald absorption with iron-related components characteristic of aquamarine. Principal iron features occur near 835 nm for divalent iron and 371 nm for trivalent iron. Chromium absorption is modified by overlapping iron bands, and observed pleochroism ranges from yellowish green in the ordinary direction to greenish blue or blue in the extraordinary direction. Longer-wavelength near-infrared absorptions are assigned to water molecules within structural channels. Characteristic inclusions comprise brown mica and unevenly distributed greenish-brown tremolite–actinolite rods and needles, commonly with a bamboo-like appearance. Colourless prismatic inclusions aligned with the c-axis and associated fluid inclusions resemble features of Brazilian emeralds from Belmont and Capoeirana, although the Malagasy material shows less fluid-inclusion diversity. Liquid–gas inclusions predominate, with three-phase and multiphase examples also present. Additional features include rounded transparent crystals, opaque grains and plates, healed or partly healed fractures, localized inclusion concentrations, and nearly colourless cores surrounded by green rims.