Garnet Varieties: Gemstone Information 

The word ‘garnet’ is known from antiquity and is derived from the Latin word granatum – pomegranate, which in turn derives from granum – grain; meaning multi-seeded in the context of the pomegranate, the seeds of which turn a deep wine-red when ripe. The open fruit shows similar coloured seeds and surrounding pith, thus the allusion to the resemblance with the mineral. The name garnet is applied to a complex group of minerals that have common crystal structure and some similarity in chemical composition.Garnets Varieties present a complex classification problem, since their chemical composition is a continuous admixture of end-member components, with few (if any) natural breaks that can be used to distinguish among gemmologically significant varieties. Varieties have been defined (Stockton and Manson) as subdivisions of a species that may be differentiated either by distinctive physical characteristics such as colour and phenomena or by consistent minor chemical disparity; however, some subjectivity is still prevalent and this gives rise to uncertainty. They have similar crystal lattice structure (isostructural) and can, with the exception of the hydrogarnets (hibschite and katoite), be expressed by the general formula A3B2(SiO4)3. Within the garnet group, the mineral species approved by the International Mineralogical Association’s Commission on New Minerals and Mineral Names (CNMMN) are:

Almandine            Fe32+Al2(SiO4)3
Andradite              Ca3Fe23+(SiO4)3
Calderite                (Mn2+,Ca)3(Fe3+,Al)2(SiO4)3
Goldmanite           Ca3(V,Al,Fe3+)2(SiO4)3
Grossular               Ca3Al2(SiO4)3
Hibschite               Ca3Al2(SiO4)3-x(OH)4x (where x is between 0.2 and 1.5)
Henritermierite   Ca3(Mn,Al)2(SiO4)2(OH)4
Katoite                   Ca3Al2(SiO4)3-x(OH)4x (where x is greater than 1.5)
Kimzeyite              Ca3(Zr,Ti)2(Si,Al,Fe3+)3O12
Knorringite           Mg3Cr2(SiO4)3
Majorite                 Mg3(Fe,Al,Si)2(SiO4)3
Morimotoite         Ca3TiFe2+Si3O12
Pyrope                   Mg3Al2(SiO4)3
Schorlomite          Ca3Ti24+Fe2 3+Si)O12
Spessartine           Mn32+Al2(SiO4)3
Uvarovite              Ca3Cr2(SiO4)3
Pyralspite series
(A site replacement element)
Pyrope Mg
Almandine Fe32+
Spessartine Mn32+
Ugrandite series
(B site replacement element)
Cr Uvarovite
Al Grossular
Fe23+ Andradite