corundum, beryl, emerald, inclusions, synthetic beryl, emerald, gems

This illustrated series presents gemstone inclusions as practical evidence for identification, distinguishing natural from synthetic stones, and interpreting the conditions under which gems formed. Drawn from Gübelin’s photomicrographic studies and a collection of Kodachrome transparencies supplied to the Gemological Institute of America, the installments combine explanatory text with photographs and descriptive captions. Microscopic examination, particularly with dark-field illumination, reveals structures that may be overlooked or misinterpreted with a loupe. The sapphire section illustrates oriented needles and silk, angular growth zoning, mineral crystals, fluid cavities, and featherlike networks. Examples include hematite plates, enclosed corundum crystals, and cavities containing liquid and gas. These features are compared with curved growth striae and gas bubbles in synthetic sapphire. Gübelin cautions that appearances can be deceptive: natural cavities may resemble bubbles, while the curvature of synthetic growth lines may be difficult to recognize within a small field of view. The ruby installment similarly contrasts natural rutile arrangements, straight structural features, mineral inclusions, and fluid-related formations with curved striae and concentrations of gas bubbles in synthetic material. Zircon inclusions surrounded by halos and intersecting rutile needles illustrate characteristic internal features of individual specimens from Sri Lanka and Myanmar. The emerald section describes enclosed crystals, irregular cavities, and inclusions containing liquid, gas, and a solid phase, while comparing these with wispy formations and other internal features observed in synthetic emeralds. The diamond installment demonstrates the importance of illumination when interpreting dark inclusions: objects commonly regarded as black or carbonaceous may prove to be transparent crystals when examined appropriately. Photographs show enclosed crystals, including diamond, together with cleavage features and fractures associated with inclusions or extending inward from the surface. Subsequent installments broaden the survey to additional sapphires and other gem materials. Illustrated examples include fine networks of channels, negative crystals, mineral plates, zircon-associated halos, liquid inclusions with mobile bubbles, and cavities containing separate liquids. Topaz and tourmaline provide further examples of fluid-bearing inclusions, while the concluding selection extends the illustrated material to emerald, peridot, quartz, garnet, and moldavite. Biotite flakes in peridot and fibrous actinolite in quartz demonstrate the variety of solid inclusions; a fluid-bearing negative crystal in citrine reproduces the host’s prismatic form. Throughout the series, the diagnostic value lies in the combined character, arrangement, and appearance of internal features rather than in an isolated resemblance. Gübelin advocates making inclusion study an early part of gem examination, potentially preceding routine measurements of physical and optical properties. The series also emphasizes the scientific and aesthetic interest of microscopic structures, presenting gemstone interiors as records of mineral growth and subsequent events as well as aids to identification.