High-temperature heated blue sapphire from Sri Lanka
Micrographs

High-temperature heated blue sapphire from Sri Lanka

The rounded white crystal on the right was a zircon (ZrSiO4). In the discoid fracture (now healed) caused by the expansion of the zircon (probably metamict), the residues observed are the product of the dissociation of the zircon, mainly SiO2 glass and zirconium oxide ZrO2.