Gadolinium gallium garnet

Gadolinium gallium garnet (GGG, Gd₃Ga₅O₁₂) is a synthetic crystalline material of the garnet group, with good mechanical, thermal, and optical properties. It is typically colorless. It has a cubic lattice, a density of 7.08 g/cm³ and its Mohs hardness is variously noted as 6.5 and 7.5. Its crystals are produced with the Czochralski method. During production, various dopants can be added for colour modification. The material is also used in fabrication of various optical components and as a substrate material for magneto–optical films (magnetic bubble memory).^[2] It also finds use in jewelry as a diamond simulant. GGG can also be used as a seed substrate for the growth of other garnets such as yttrium iron garnet.^[3]

Another interesting aspect to this synthetic gemstone is that it exhibits both fluorescence under UV, and phosphorescence (glow-in-the-dark) properties.

It is produced by the Czochralski method using Gallium(III) oxide and Gadolinium(III) oxide.^[4] This is usually done at 2000 degrees C in an iridium crucible. The cost of a GGG wafer comes from refining the starting oxides to a purity of at least 99.9%.^[5]