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Occurs in Pinal County. Common in Arizona.

Andradite garnet
Andradite garnet. Al Copley photo.

Chemical Formula: Ca3Fe2(SiO4)3

Specific Gravity: 3.8-4.1

Luster: Vitreous to resinous

Hardness: 6.5-7

Andradite is a mineral within the garnet group known for its various colors and crystal forms. Its presence in skarn deposits and its value as a gemstone make it of interest in both geological and aesthetic contexts.

Next Pinal County mineral: Anglesite

MinDat Andradite

Andradite is a mineral that belongs to the garnet group, which is a family of silicate minerals. It is recognized for its various colors, including shades of green, yellow, brown, and black. The name “andradite” is in honor of José Bonifácio de Andrade e Silva, a Brazilian mineralogist.

The chemical formula for andradite varies based on the specific composition, but it is generally represented as Ca3Fe2(SiO4)3. This indicates its composition of calcium (Ca), iron (Fe), silicon (Si), and oxygen (O). Andradite often contains varying amounts of other elements, such as aluminum, manganese, and titanium.

Andradite crystals can exhibit different crystal habits, including dodecahedral, trapezohedral, and rhombic dodecahedral forms. The mineral forms in a variety of geological settings, including metamorphic rocks, igneous rocks, and skarn deposits.

One notable variety of andradite is “demantoid,” which is a green gemstone with a high dispersion, often referred to as “fire.” Demantoid is highly valued by collectors and gem enthusiasts due to its brilliance and rarity.

Andradite is often associated with skarn deposits, which form at the contact between igneous intrusions and carbonate rocks. These deposits can contain valuable minerals such as garnet, pyroxene, and various ores. Andradite’s presence in skarns can provide important clues about the mineralogical and geological history of these deposits.