gems, spinel, spinel inclusions, root-like inclusions

G.R. Crowningshield records unusual inclusion features observed during examination of natural pink and red spinels at the Gemological Institute of America’s New York laboratory. The note places these observations in the context of increasing consumer familiarity with pink and red spinel and their more frequent appearance in the gem trade, both locally and in East Asia. Several lots, together weighing hundreds of carats, provided the material examined. Among these collections, two stones attracted particular attention because their inclusions differed from the forms more commonly encountered in natural spinel. One contained branching, root-like inclusions whose appearance recalled features previously observed in diamond, another mineral of the cubic crystal system. Earlier published diamond observations are cited as visual comparisons, without establishing that the inclusions in the two host minerals have the same composition or origin. A second spinel contained a series of rounded, frosted-looking features likened to tennis balls. These are identified as negative crystals, despite their superficial resemblance to gas bubbles in slag glass. The comparison concerns their microscopic appearance rather than an identification of the spinel as glass or of the cavities as ordinary gas bubbles. A third illustration provides a contrast by showing more familiar inclusions, including octahedral forms, in a red spinel. Three photomicrographs accompany the account: root-like inclusions photographed with dark-field illumination at 20× magnification, rounded negative crystals at 30×, and common natural-spinel inclusions, also at 30×. Together, the images document both unusual branching structures and rounded cavities alongside the more recognisable octahedral forms. The report is descriptive and does not assign a mineral species to the root-like inclusions, specify the contents of the negative crystals, or propose a formation mechanism for either unusual feature. Its principal contribution is to broaden the documented range of inclusion appearances in natural spinel and to distinguish the observed negative crystals from the bubble-like features they visually resemble.