Rainbow-Colored Partially Healed Fissure in Blue Sapphire
Thin-film interference caused by inclusions occasionally produces attractive scenes. In a 4.13 ct untreated blue sapphire from Sri Lanka, a partially healed fissure displayed vibrant iridescent colors due to this phenomenon under fiber-optic illumination (see above).
Healed fissures, known as fingerprints or feathers in gemology, are created by the natural healing process of surface-reaching fractures in the host gem material. Generally, when fluid involved in the healing process is trapped, fluid-filled inclusions such as negative crystals or thin internal fissures are formed (e.g., E. Roedder, “Ancient fluids in crystals,” Scientific American, Vol. 207, No. 4, 1962, pp. 38–47). When the trapped fluid is thin enough, the difference in refractive index between the fluid and the host material causes thin-film interference and may result in vibrant colors.
Healed fissures are common in various gemstones and sometimes display iridescence (e.g., Spring 2021 G&G Micro-World, p. 68; Summer 2023 G&G Micro-World, p. 227). In this sapphire, the combination of a brushstroke-like texture and rainbow colors in a gradation from red to indigo produces a spectacular scene.
