Fissure with Moiré Pattern in Spinel
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 rare to see them expressed in such a spectacular form.
