corundum, inclusions.5, gems

Examines the scientific basis, practical requirements and limitations of determining the geographical origin of gemstones, emphasising that locality names should describe provenance rather than colour or quality. Hänni distinguishes a gemstone’s deposit of origin, whether primary or secondary, from commercial associations attached to names such as Myanmar, Kashmir or Pailin. Deposits produce variable material, and visually similar stones can occur in different regions; consequently, appearance alone cannot establish origin. Reliable attribution requires characteristics that support a proposed source while excluding alternatives, preferably through at least three independent diagnostic features involving inclusions, spectroscopy and trace-element composition. The paper relates such characteristics to the conditions of crystal formation, including available constituents, growth rate, fluid chemistry, oxidation state, temperature, pressure and deformation history. These processes influence growth zoning, twinning, colour distribution, mineral and fluid inclusions, healed fissures and trace-element patterns. Methods reviewed include microscopy in air and immersion, microthermometry, ultraviolet–visible and infrared spectroscopy, energy-dispersive X-ray fluorescence, electron-microprobe analysis, scanning electron microscopy, Raman spectroscopy and magnetic-resonance techniques. Their complementary roles range from documenting internal structures to identifying enclosed minerals and measuring chemical differences among gemstone populations. Particular importance is assigned to comprehensive reference collections of securely sourced specimens, analytical records, geological information and current literature. Ideally, comparison material should be collected directly from deposits; where this is impossible, reliable museum or historical collections may provide alternatives. Reference collections must represent variation within individual sources as well as differences between them. Examples demonstrate that features once regarded as exclusive can lose diagnostic status: three-phase inclusions formerly associated principally with Colombian emeralds also occur in material from Australia and Nigeria, requiring additional chemical evidence. Attribution is restricted when stones lack diagnostic features, properties overlap among deposits, jewellery settings obstruct examination, source information is inadequate or heating has destroyed useful evidence. Political borders may divide geological deposits, while individual countries may contain several distinct sources, complicating the wording of conclusions. Origin determinations therefore remain expert opinions expressing the most probable interpretation of available evidence. Their reliability depends on equipment, experience, continually revised reference data and prudent interpretation. Where observations are insufficient or ambiguous, the author argues that a definite origin report should not be issued.