Garnet

Garnet is the birthstone for January and is a mineral with various types and beauties. It is generally divided into two main categories: the red series (pyralspite) and the green series (ugrandite).

Many commercial names are not listed as formal names on identification reports, so a basic knowledge of names may be necessary. Interestingly, color-change garnets, especially the bluish-green Bekily blue garnet, belong to the red series, while hessonite, which exhibits orange to red colors with a molasses-like structure, belongs to the green series. There are also "Alexandrite-type" garnets that have a strong green body color and show a red color change effect; these are also a type of color-change garnet.


Below are various garnet values.
Name: Garnet
Japanese name: Zakuroishi
Chemical formula: X3Y2(SiO4)3
* The type is determined by the elements in X/Y.
Crystal system: Isometric
Specific gravity: 3.5 - 4.3
Mohs hardness: 6.5 - 7.5
Cleavage: None
Luster: Vitreous
Transparency: Transparent to translucent
Refractive index: 1.72 - 1.94
Birefringence: None
Color: Red series, Green series, Colorless
Dispersion: 0.022 - 0.057