Garnet
| Garnet | |
|---|---|
| General | |
| Category | Nesosilicate |
| Formula | The general formula X3Y2(SiO4)3 |
| IMA symbol | Grt |
| Crystal system | Isometric |
| Crystal class | |
| Space group | Ia3d |
| Identification | |
| Color | virtually all colors, blue is rare |
| Crystal habit | Rhombic dodecahedron or cubic |
| Cleavage | Indistinct |
| Fracture | conchoidal to uneven |
| Mohs scale hardness | 6.5–7.5 |
| Luster | vitreous to resinous |
| Streak | White |
| Diaphaneity | Can form with any diaphaneity, translucent is common |
| Specific gravity | 3.1–4.3 |
| Polish luster | vitreous to subadamantine |
| Optical properties | Single refractive, often anomalous double refractive |
| Refractive index | 1.72–1.94 |
| Birefringence | None |
| Pleochroism | None |
| Ultraviolet fluorescence | variable |
| Other characteristics | variable magnetic attraction |
| Major varieties | |
| Pyrope | Mg3Al2Si3O12 |
| Almandine | Fe3Al2Si3O12 |
| Spessartine | Mn3Al2Si3O12 |
| Andradite | Ca3Fe2Si3O12 |
| Grossular | Ca3Al2Si3O12 |
| Uvarovite | Ca3Cr2Si3O12 |
Garnets ( /ˈɡɑːrnɪt/) are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives.
Garnet minerals, while sharing similar physical and crystallographic properties, exhibit a wide range of chemical compositions, defining distinct species. These species fall into two primary solid solution series: the pyralspite series (pyrope, almandine, spessartine), with the general formula [Mg,Fe,Mn]3Al2(SiO4)3; and the ugrandite series (uvarovite, grossular, andradite), with the general formula Ca3[Cr,Al,Fe]2(SiO4)3. Notable varieties of grossular include hessonite and tsavorite.