Siderite (FeCO₃) is the iron-rich member of the calcite-group carbonate trio (with calcite, magnesite, rhodochrosite). It forms in sedimentary banded iron formations, hydrothermal veins, and carbonate-replacement zones. Collector specimens favor sharp tan-to-honey rhombohedral crystals, often with iridescent oxidation rinds. The Mt. Saint-Hilaire (Quebec) and Panasqueira (Portugal) localities supply gem-grade material.
Key Facts
- Mohs hardness 3.5–4.5.
- Trigonal; isostructural with calcite, dolomite, rhodochrosite.
- Tan to dark brown color from Fe; weathers iridescent or dull.
- Major iron ore in sedimentary banded iron formations and Clinton-type ironstones.
- Forms continuous series with magnesite (Mg) and rhodochrosite (Mn).
Notable Localities
Panasqueira (Portugal) and Mt. Saint-Hilaire (Quebec) yield gem-grade rhombohedrons. Hunan and Jiangxi host Chinese collector specimens.
Found at these Localities
- Rapid Creek (Yukon) (育空地区急流溪磷酸盐产地)
- Siegerland District (西格兰铁矿区)
- Příbram (普日布拉姆银矿)
- Cornwall Mining District (康沃尔矿区)
- Panasqueira (帕纳斯凯拉钨矿)
- Llallagua (Siglo XX) (亚亚瓜矿)
- Jiangxi (江西)
- Hunan (湖南)
