Garnet Chemistry

Assorted GarnetsWhile all garnet species share the same crystal structure, they differ chemically. Garnets are divided into two groups: those that contain aluminum, and those that contain calcium as part of their basic chemistry. Aluminum garnets are generally reddish due to other trace elements such as magnesium, iron and manganese. Calcium garnets are generally green, orange and yellow due to trace elements such as chromium, iron and aluminum.

As I mentioned in a previous post, there are 5 significant gem species of garnet, however, some garnets actually are a mixture of two or more garnet species. This mixture is due to a chemical substitution within the crystal structure of a mineral. For example, Rhodolite is a mixture of pyrope and almandite.

Photo: Provided by the American Gem Trade Association.
Author: Michelle M. Rahm is a GIA-trained Graduate Gemologist and is President of Colorado’s Mile High Chapter of the GIA Alumni Association. She has been selling gemstones and jewelry online since 1997. Visit her websites and

About mrahm

Michelle holds a Graduate Gemologist Diploma, Graduate Diamonds Diploma and Graduate Colored Stones Diploma through the Gemological Institute of America's distance education program. Michelle currently serves as President of the Mile High GIA Alumni Association. She also serves on the board of the Rocky Mountain Jeweler's Association and is a member of the American Gem Trade Association.
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