Arrow-Patterned Negative Crystals in Sapphire
Negative crystals arrayed in an arrow-like pattern. Photomicrograph by Suwasan Wongchacree; field of view 1.07 mm.
Negative crystals are a common inclusion in corundum and often rupture upon exposure to moderate heat treatment. The author recently analyzed a sapphire containing a series of negative crystals arranged in an arrow-like pattern (see above). Careful examination revealed a partially healed fissure intersecting one of the negative crystals, indicating the stone had been subjected to heat treatment.
Fortunately, this spectacular pattern of negative crystals endured the heat treatment process, decorating the internal micro-world of this sapphire.
