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Types of Garnet Rocks

Garnets are a group of neosilicate minerals, of which there are many types. Altogether, these types are classified collectively as the "garnet group." This group's overall chemical formula is X3Y2(SiO4)3. X and Y each represent places where one of several elements may get mixed in when the garnet is forming.

The different types of garnets are classified into species. The most commonly known species within the garnet group include pyrope, uvarovite, almandine, grossularite, andradite and spessartine.

Pyrope
- Pyrope is a silicate containing magnesium and aluminum, having a chemical formula of Mg3Al2Si3O12. The coloration of pyrope is a dark (or black) red. The main places pyrope can be found are in the Czech Republic (from the area called Bohemia), Norway, South Africa and Arizona. It can also be found in Australia, Argentina, Myanmar and Brazil.
  
  One type of pyrope (from Tanzania and Norway) shows color change. It turns from violet in sunlight to red in artificial light.
Uvarovite
- Named after Count Sergey Semyonovich Uvarov by Germain Henri Hess in 1832, uvarovite is bright green calcium chromium silicate whose chemical formula is Ca3Cr2Si3O12. It is the only known garnet to be consistently green. Uvarovite sources include Russia, Canada, Finland, Spain, South Africa and Norway.
Almandine
- Almandine (Fe2+3Al2Si3O12) is a violet-red to brown-red or dark red iron aluminum silicate that is the most common of all types of garnets. The main place it comes from is India, but it also comes from Idaho, Alaska, New York, North Carolina, Brazil and Sri Lanka.
Grossularite
- With a chemical composition of Ca3Al2Si3O12, grossularite is a calcium aluminum silicate. It is ideally a bright green gem, but can also come in such colors as yellow, light brown or pink. Locations of grossularite include Vermont, Canada, Brazil, Mexico, Sri Lanka, Tanzania, Kenya and Pakistan.
Andradite
- A garnet species whose only important variety is demantoid, andradite (Ca3Fe2Si3O12) is a calcium iron silicate whose hardness is less than that of red-colored garnets (6.5 on the Mohs scale of hardness in comparison to 7 or 7.5). Andradite can be found in Russia, Italy, Zaire, Mexico and Switzerland.
Spessartine
- Once called spessartite, spessartine (Mn3Al2Si3O12) is a manganese aluminum silicate. It belongs to the isometric crystal system, and within that system it takes a hexoctahedral shape. Colors of spessartine range from red (at times red-violet) to orange or yellow. Sources of spessartine have been California, Virginia and Brazil. Other sources have been Norway, Idaho, Pakistan, Sri Lanka, Myanmar, Australia and Madagascar.

Gemology