Crystal structure
Garnets are nesosilicates with the general formula X3Y2(SiO4)3. The X site is usually occupied by divalent cations (Ca, Mg, Fe2+) and the Y site by trivalent cations (Al, Fe3+, Cr). The chemical elements in garnet include calcium, magnesium, aluminium, iron2+, iron3+, chromium, manganese, and titanium. Garnets are most often found in the dodecahedral crystal habit, but are also commonly found in the trapezohedron habit. They crystallize in the isometric system, having three axes that are all of equal length and perpendicular to each other. Garnets do not show cleavage, so when they fracture under stress, sharp irregular pieces are formed
Garnets are nesosilicates with the general formula X3Y2(SiO4)3. The X site is usually occupied by divalent cations (Ca, Mg, Fe2+) and the Y site by trivalent cations (Al, Fe3+, Cr). The chemical elements in garnet include calcium, magnesium, aluminium, iron2+, iron3+, chromium, manganese, and titanium. Garnets are most often found in the dodecahedral crystal habit, but are also commonly found in the trapezohedron habit. They crystallize in the isometric system, having three axes that are all of equal length and perpendicular to each other. Garnets do not show cleavage, so when they fracture under stress, sharp irregular pieces are formed
Hardness
Because the chemical composition of garnet varies, the atomic bonds in some varieties are stronger than in others. As a result, the mineral shows a range of hardness on the Mohs Scale of about 6.5 to 7.5. The harder varieties, like almandite, are often used for abrasive purposes.
Garnet group endmembers
Pysalspite garnets - Al in B site
Almandine: Fe3Al2(SiO4)3
Pyrope: Mg3Al2(SiO4)3
Spessartine: Mn3Al2(SiO4)3
Source from Wikipedia
No comments:
Post a Comment