About
Siderite is easily altered to iron oxides. A brown Goethite replacement of Siderite is common. Limonite, an amorphous mineral, is commonly found in rhombohedral crystals, as it frequently pseudomorphs after Siderite.
Concretionary Siderite nodules are noted for containing a wide variety of flora and fauna fossils, especially in the open-pit coal mining operations of eastern Illinois and western Indiana, where these concretions are common in the rock removed before the coal veins are exposed.
Crystal Forms & Aggregates
Complex Tests
2) Effervesces in hot hydrochloric acid.
Striking Features
Environment
Varieties
✓ common · ✗ uncommon
- Sphaerosiderite— Spherulitic variety of Siderite, forming rounded masses from radiating crystals.
- Clay Ironstone— Concretionary variety of Siderite.
- Oligonite— Oligonite, also known as Oligon Spar, is a manganese rich variety of Siderite, containing a greater amount of iron over manganese. Its chemical formula is (Fe,Mn)CO3.
- Sideroplesite— Sideroplesite, also known as Magniosiderite, is a magnesium rich variety of Siderite, containing a greater amount of iron over magnesium. Its chemical formula is (Fe,Mg)CO3.
Uses
Noteworthy Localities
Platy Siderite crystals have been abundant in China at the Yaogangxian Mine, Hunan Province. Odd, ball shaped Siderite has come from Dal'negorsk, Primorskiy Kray, Russia. Excellent Siderite pseudomorphs after Calcite come from Aggeneys, Northern Cape Province, South Africa.
In South America, some of the best examples of this mineral, in transparent gemmy form, is Morro Velho, Nova Lima, Minas Gerais, Brazil. Large and usually dark brown crystals come from the Julcani District, Huancavelica, Peru; and modified gemmy crystals from the Siete Suyos Mine, Atocha-Quechisla, Potosi, Bolivia. In Ivigtut, Greenland, Siderite crystals were found associated with the rare mineral Cryolite. Canada has produced excellent examples of this mineral at Mont St. Hilaire, Quebec.
In the U.S., good Siderite comes from a vein in Roxbury, Litchfield Co., Connecticut, with some specimens altered to Limonite. Excellent crystals have been found in the Eagle mine, Gilman Co., Colorado; Bisbee, Cochise Co., Arizona; Kellogg, Shoshone Co., Idaho; and Hiddenite, Alexander Co., North Carolina.
Common Mineral Associations
Distinguishing Similar Minerals
Calcite - Lighter in weight.
Sphalerite - Different cleavage, doesn't effervesce in hydrochloric acid, does not become magnetic when heated.
Chabazite - Usually occurs in different mineral environments.
Photos
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