Garnets

Garnet minerals are great group of silicate minerals with general chemical formula X3Y2Si3O12. X stands for divalent Ca, Mg, Fe and Mn cations and Y – for trivalent Al, Fe and Cr cations. There are two main groups of garnet minerals. One group is Uvarovite (Ca3Cr2Si3O12) – Grossular (Ca3Al2Si3O12) – Andradite (Ca3Fe2Si3O12) group. This group is called Ugrandite (based on the beginnings of garnet minerals names within this group). This group has calcium in X position and chromium, aluminum or iron in Y position. Uvarovite, Grossular and Andradite are end members of this group, but mixed compositions (example: Ca3(Al, Fe)Si3O12) are also common.

Another group: Pyrope (Mg3Al2Si3O12) – Almandine (Fe3Al2Si3O12) – Spessartine (Mn3Al2Si3O12).  This group is called Pyralspite group. This group has aluminum in Y position and magnesium, iron or manganese in X position. All these three minerals can also blend with each other and form mixed minerals. Also, minerals of this group can blend to Grossular through calcium – magnesium, iron or manganese cations exchange.

This illustration shows those relations. At the peaks there are end members shown and those end members which blend to each other are connected. The amount of minerals at the end parts and at the mixture parts does not represent any mineral abundancy data. The enhancement at the peaks is just for illustration purpose.

I’ve chose one color for each garnet mineral. I’ve used more common color for each garnet, but it is important to note that garnet mineral colors have greater variety. And some garnets in its pure form is even colorless.

I’ve also used only one mineral crystal shape when there are more.

This scheme is not suited for professional studies. Other, more comprehensive mineralogy or geochemistry sources should be used if one studies garnet minerals professionally. This scheme is useful for geology or mineralogy beginners, enthusiasts or even for professional geologists as science-based eye appealing and fun illustration.

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