gems, beryl, emerald, Colombia, Muzo, trapiche emerald

Mr E. Bertrand then presented some rather curious emerald crystals; these specimens come from Muzo, New Granada. They consist, at the centre, of an almost colourless hexagonal portion; this central part is surrounded by another, green portion, striated parallel to the sides of the hexagon and showing modifications tangent to the edges of the prism. The central part shows to the naked eye a six-rayed asterism and the parhelic circle; under the polarising microscope, in convergent light, the cross and rings can be seen, with a slight dislocation in the three directions normal to the sides of the hexagon. The striated green portions surrounding the central core show to the naked eye a single luminous line perpendicular to the striations. In convergent polarised light, the cross and rings are consistently deformed and show a phenomenon similar to that which would be produced by a crystal with two closely spaced optic axes, the plane of the axes being perpendicular to the striations. These crystals, numbering about forty, all show the same phenomenon. First mention of trapiche emeralds at Muzo.