corundum, Burma.12, gems

A broad introductory lecture on precious stones, written from the practical viewpoint of a mining engineer familiar with Burma’s gem industry. Morgan discusses the qualities that give gems value—beauty, durability, hardness, transparency, color, rarity, and fashion—and surveys the principal precious and semiprecious stones, including diamond, ruby, sapphire, emerald, opal, spinel, tourmaline, aquamarine, chrysoberyl, peridot, garnet, beryl, zircon, amethyst, moonstone, turquoise, jadeite, and lapis lazuli. His treatment of ruby is especially notable, drawing on experience with the Burma Ruby Mines and giving contemporary observations on value, color, size, production, and the Mogok deposits; he notes that rubies occur chiefly in residual clays and gravels derived from crystalline limestone. He also discusses sapphire, spinel, and tourmaline from Burma and gives particular attention to jadeite, emphasizing its occurrence in northern Burma and its strong Chinese market. Morgan outlines methods of gem recovery from residual deposits, stresses the large scale required for profitable gem mining, and compares ruby mining with diamond recovery. The lecture concludes with remarks on glass, reconstructed and synthetic gems, practical methods of gem identification using hardness, specific gravity, pleochroism, and refractive index, and a tabular summary of the characteristics and principal sources of important gemstones.