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Siderite Mineral Facts:

Chemical Formula: Fe₂CO₃

Colors: Normally yellow to brown. Sometimes white. Streak is white.

Hardness: 3.5 to 4.0

Density: 4.5 to 5

Cleavage: Perfect rhombohedral cleavage (cleavage angle = 107).

Crystallography: Hexagonal-rhombohedral.

Luster:. Vitreous luster.

Optics: (Refractive Index): w=1.875; e=1.633

Composition, Structure and Associated Minerals:
Siderite is found in the form of clay ironstone and black-band ore in extensive stratified formations associated with coal measures. These ores are the chief source of iron in Great Britain and are found in Staffordshire, Yorkshire and Wales. Clay ironstone is also abundant in the coal measures of western Pennsylvania and eastern Ohio, but it is not used to any great extent as an ore. Siderite, in its crystallized form, is a common vein mineral associated with various metallic ores, as silver minerals, pyrite, chalcopyrite, tetrahedrite, galena, etc.

Identification and Diagnostics
Recognized usually by its effervescence in acids, color and cleavage. Difficultly fusible (4.5-5). Becomes strongly magnetic on heating. Soluble in hydrochloric acid with effervescence; solution gives with potassium ferricyanide a dark blue precipitate (test for ferrous iron).

Occurrence, Localities and Origins:
Siderite is an important iron ore in some parts of the world (especially Great Britain), though not as much used as formerly.It is found crystallized and massive, in botryoidal and globular forms and in earthy masses. The mineral changes on exposure into limonite and sometimes into hematite or even into magnetite.

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