corundum, inclusions.5, gems

A detailed continuation of Isaac Lea’s earlier studies of microscopic inclusions in gemstones and minerals. Drawing on an enlarged personal collection, Lea examines cavities, fluid inclusions and minute enclosed crystals in sapphire, ruby, spinel, emerald, beryl, zircon, moonstone and other gem materials. Of particular importance is his observation that fine sapphires commonly contain abundant acicular crystals and cavities; he relates the oriented needles directly to the intersecting bands that produce the star in asteriated corundum. He also describes inclusions in North Carolina corundum, Ceylon sapphires and spinels, emeralds containing fluid-filled cavities with enclosed cubic crystals, and other distinctive internal features, illustrating many of them on two plates. The paper is an important early contribution to gemstone microscopy and to the recognition of inclusions as diagnostic evidence of a gem’s internal structure and growth history.