Fissure with Moiré Pattern in Spinel
Tyler Smith
A precipitation of an unidentified mineral in a fissure of a purple spinel creates this highly intricate moiré pattern. A combination of oblique fiber-optic and darkfield illumination was used. Photomicrograph by Tyler Smith; field of view 2.90 mm.
"Surface-reaching fissures commonly host precipitates of epigenetic minerals, as was the case with a 4.22 ct purple spinel recently examined by the author. “Islands” of unidentified birefringent inclusions occupied a near-planar fissure. These inclusions were inert to Raman spectroscopy. Delicate depositions radiating from these islands interacted to create a complex moiré pattern (see above). Moiré patterns, named after their resemblance to a type of fabric, form when parallel or concentric lines overlap. It is unclear whether the islands formed first and were partially dissolved in a secondary event, or if they formed simultaneously with the spinel. Although moiré patterns have been observed in partially healed fluid fingerprints and surface-reaching fissures, it is ... "
https://www.gia.edu/gems-gemology/fall- ... -in-spinel
