Sideritt

Sideritt, or siderite (FeCO3), is a carbonate mineral that forms in a variety of geological settings. It commonly occurs in sedimentary rocks as diagenetic precipitates and concretions, and also in hydrothermal ore veins. Siderite crystallizes in the rhombohedral system, typically producing rhombohedral or tabular crystals, but more often appearing as massive, earthy nodules or layers. Colors range from pale brown to yellow-brown; crystals may be colorless or greenish when finely zoned. The streak is pale yellow, and the luster is vitreous to earthy. It has a Mohs hardness of about 3.5–4 and a specific gravity around 3.9–4.0. It readily effervesces in cold dilute acids due to its carbonate composition and often exhibits rhombohedral cleavage.

Formation and occurrence: Siderite forms by the diagenetic precipitation of Fe2+ and CO3^2− in reducing environments, sometimes replacing carbonate rocks or forming concretions around organic matter. It is commonly associated with calcite, dolomite, quartz, pyrite, goethite, and other iron minerals. It occurs worldwide, including in the Carpathians, Central Europe, and in sedimentary iron ore deposits in North America and South America.

Use: Siderite is an important iron ore in certain deposits where hematite or magnetite are not abundant, although its iron content and the presence of carbonate lower processing efficiency; high-grade siderite concentrates are used for steelmaking after beneficiation.

Etymology: The name derives from the Greek sideros, iron.