Ankerite - Encyclopedia

    Class : Carbonates, Nitrates, Borates
    Subclass : Anhydrous carbonates
    Crystal system : Rhombohedral
    Chemistry : CaFe(CO₃)₂
    Rarity : Very common

Ankerite is a common carbonate of iron and calcium which forms a series with dolomite. It is a fairly common matrix mineral in medium and low temperature hydrothermal veins, associated with dolomite, calcite, siderite and various sulphides. It is the dominant carbonate in the Precambrian iron formations ("algoma" type ores). It is also known in saliferous marls, associated with dolomite. Its name was given to it in honor of the Austrian mineralogist Mathias Joseph Anker. Ankerite generally occurs in often striated rhombohedral crystals, more rarely in prisms, in tabular or pseudo-octahedral crystals, never in scalenohedra; sometimes in lamellar aggregates with curved faces called "saddle", facies also very common for dolomite. Ankerite is also massive. Transparent to translucent, it has a vitreous luster, and is usually yellowish to brown, sometimes salmon-coloured, which changes superficially to blackish-brown by atmospheric weathering into goethite. Ankerite benefits from restricted use in the construction industry, where it is used in the manufacture of certain cements and refractories. It has constituted a poor quality iron ore in countries lacking this metal or during difficult periods in history.

Twins are numerous and common for ankerite, especially on {0001}, on {1010} and on {1120}.

No fake identified for this mineral species but very difficult to differentiate from dolomite and siderite without chemical analysis.