The crystallographic structure of garnets has been expanded from the prototype to include chemicals with the general formula A3B2(C O4)3. Besides silicon, a large number of elements have been put on the C site, including Ge, Ga, Al, V and Fe.
Yttrium aluminium garnet (YAG), Y3Al2(AlO4)3, is used for synthetic gemstones. Due to its fairly high refractive index, YAG was used as a diamond simulant in the 1970s until the methods of producing the more advanced simulant cubic zirconia in commercial quantities were developed. It can be grown in a variety of colors: Colorless, green, pink, blue, yellow, lavender, etc. When doped with neodymium (Nd3+) these YAl-garnets are useful as the lasing medium in lasers. Some YAG lasers use others colored cations (Cr, Ho ...).
Interesting magnetic properties arise when the appropriate elements are used. In yttrium iron garnet (YIG), Y3Fe2(FeO4)3, the five iron(III) ions occupy two octahedral and three tetrahedral sites, with the yttrium(III) ions coordinated by eight oxygen ions in an irregular cube. The iron ions in the two coordination sites exhibit different spins, resulting in magnetic behaviour. YIG is a ferrimagnetic material having a Curie temperature of 550 K.
Another example is gadolinium gallium garnet, Gd3Ga2(GaO4)3 which is synthesized for use in magnetic bubble memory.
