Occurs in Pinal County.
Chemical Formula: CaFe(CO3)2
Specific Gravity: 3.1-3.3
Ankerite is a carbonate member of the dolomite group. It is named after the Austrian mineralogist Matthias Joseph Anker. Ankerite is often found as a secondary mineral in various geological environments, including hydrothermal veins, sedimentary rocks, and metamorphic rocks.
Key characteristics of ankerite include:
- Composition: Ankerite has a chemical formula of Ca(Fe,Mg,Mn)(CO3)2. This formula indicates that ankerite can contain a combination of calcium (Ca), iron (Fe), magnesium (Mg), and manganese (Mn) in its structure. The relative proportions of these elements can vary, leading to different compositions of ankerite.
- Color and Luster: Ankerite typically has a brownish, reddish, or grayish color. Its luster can range from vitreous (glassy) to submetallic. The color variations are often due to the presence of different metal ions in its crystal lattice.
- Crystal Structure: Ankerite crystallizes in the trigonal crystal system. Its crystal structure is similar to that of calcite and dolomite, both of which are carbonate minerals. Ankerite’s structure consists of carbonate ions (CO3) combined with metal ions.
- Habit: Ankerite can form a variety of crystal habits, including rhombohedral, scalenohedral, and tabular crystals. However, it is more commonly found as fine-grained aggregates, nodules, or massive forms.
- Occurrence: Ankerite is often associated with hydrothermal mineralization, where hot fluids carry dissolved minerals and deposit them as they cool. It can also occur as a replacement mineral in sedimentary rocks and metamorphic rocks.
- Economic Significance: Ankerite is not a major ore mineral itself, but it can be associated with valuable metal ores. For example, ankerite can be found in some types of iron ore deposits and is considered a gangue mineral (non-valuable mineral) in such cases.