Is siderite an ore of iron?
Is siderite an iron ore? Sometimes: FeCO3 is 48.20% iron, and BGS records primary-siderite mines in Weardale, but USGS says iron ore is almost always oxide.
Sometimes. Siderite, Fe(CO3), is a carbonate of 48.20% iron, and its Handbook sheet calls it a common component of bedded sedimentary iron ores. BGS records Weardale deposits rich in primary siderite that were workable, though most of the area’s ore became workable, up to 40% iron, only after weathering to goethite. USGS says iron ore today is almost always oxide.
In short
- What the sources say. The Handbook of Mineralogy siderite sheet: a common component of bedded sedimentary iron ores and metamorphic iron formations. British Geological Survey, British regional geology: Northern England (2010), via BGS Earthwise: iron carbonate minerals, particularly siderite and ankerite, are locally abundant in the Northern Pennine Orefield, and a number of deposits rich in primary siderite were workable, as at the Carricks, Rowantree and Rispey mines in Weardale. The USGS National Minerals Information Center iron ore page says iron ore almost always consists of iron oxides, primarily magnetite and hematite.
- The weathering upgrade. Worked from the formulas, FeCO3 (115.85) weathered to FeO(OH) (88.85) keeps all its iron and sheds a quarter of its mass: 1 kg of siderite becomes 767 g of goethite, and the iron grade rises from 48.20% to 62.85%, a factor of 1.30. BGS describes exactly that direction in the North Pennines: goethite-rich ores derived by supergene oxidation of primary iron carbonate minerals.
- Documented failure: the formula is a ceiling no ore reached. BGS gives the Weardale ores up to 40 per cent Fe, Coal Measures clay ironstones around 25 per cent, and Cumbrian haematite 50 to 60 per cent. Pure siderite is 48.20%, goethite 62.85%, hematite 69.94%. Every rock figure sits below the mineral it is named for, because ore is rock, not a single mineral.
- Is it a carbonate ore? Yes in the plain sense: the IMA formula Fe(CO3) is a carbonate, the sheet files it in the Calcite group, and BGS calls the Pennine material primary iron carbonate. The carbonate is also the handicap: 37.99% of pure siderite is CO2, by the sheet’s ideal column.
- Agreement. The 48.20% figure and the Camborne analysis’s 47.48% are those on siderite; its per-kilogram comparison is not repeated here. The magnet question is on is siderite magnetic, and the same ore-only-from-sources method on lead is on what metal is cerussite an ore of.
| Material | Formula or rock | Source | Iron by mass | What the source says about ore |
|---|---|---|---|---|
| Siderite | Fe(CO3) | IMA; Handbook sheet | 48.20%, worked | “A common component of bedded sedimentary iron ores and metamorphic iron formations” |
| Siderite, Camborne analysis | FeO 61.08% | Handbook sheet | 47.48%, worked | — |
| Goethite (siderite weathered: 767 g per kg) | FeO(OH) | IMA; Handbook sheet | 62.85%, worked | “An important component of ore in weathered iron deposits”; “an ore mineral in the Lake Superior district” |
| Hematite | Fe2O3 | IMA; Handbook sheet | 69.94%, worked | One of the primary forms of iron ore (USGS NMIC); the sheet: “a major constituent in oolitic iron formations” |
| Magnetite | Fe2+Fe3+2O4 | IMA; Handbook sheet | 72.36%, worked | One of the primary forms of iron ore (USGS NMIC); the sheet: magmatic segregation or contact metamorphism “may produce economic deposits” |
| Northern Pennine goethite-rich ores (Weardale) | Supergene oxidation of primary iron carbonate | BGS | Up to 40 per cent Fe | Worked in the 19th century; workable level usually only attained by supergene alteration; some primary-siderite deposits also workable |
| Coal Measures clay ironstones | Sedimentary ironstone | BGS | Around 25 per cent | Basis of ironworks at Consett, Bedlington, Tow Law, Witton Park |
| West and south Cumbrian haematite | Almost monomineralic haematite | BGS | 50 to 60 per cent | The region’s largest and richest iron ore deposits |
Is siderite an iron ore? What the sheet, BGS and USGS say
Siderite has been an iron ore where it was concentrated, but it is not the iron ore of today’s industry. The Handbook of Mineralogy siderite sheet gives Fe2+CO3, Calcite group, hardness 3.75–4.25, density 3.96, streak white, and calls it a common component of bedded sedimentary iron ores and metamorphic iron formations, also found in hydrothermal metallic veins, carbonatites and concretions. The September 2026 IMA-CNMNC Master List writes Fe(CO3), status A, 1962 s.p.
Britain. British Geological Survey, British regional geology: Northern England (2010), via BGS Earthwise says iron carbonate minerals, particularly siderite and ankerite, are locally abundant within the Northern Pennine Orefield; that substantial goethite-rich ores derived by supergene oxidation of primary iron carbonate occur in vein outcrops and as bodies replacing the limestone wall-rock; that their greatest exploitation came in the 19th century, when deposits such as the Rigg and West Rigg opencasts in Weardale supplied ironworks in Weardale and at Consett, Tow Law and Spennymoor; and that, although the workable level was usually only attained by supergene alteration, a number of deposits rich in primary siderite were also workable, at the Carricks, Rowantree and Rispey mines. The siderite sheet itself names no Weardale locality.
Today. The USGS National Minerals Information Center iron ore page defines iron ore as a mineral substance which, when heated in the presence of a reductant, will yield metallic iron, and says it almost always consists of iron oxides, the primary forms of which are magnetite and hematite. The USGS Mineral Commodity Summaries 2026, iron ore describes United States resources as mainly low-grade taconite-type ores from the Lake Superior district. Neither names siderite.
How much iron is in siderite? The weathering upgrade
Pure siderite is 48.20% iron; weathered to goethite the same iron is 62.85% of the mass. On standard atomic weights FeCO3 is 115.85 g/mol, of which iron is 55.845: 48.20%. The sheet’s ideal column, 62.01% FeO and 37.99% CO2, reproduces from the formula, and its Camborne analysis, FeO 61.08%, gives 47.48% iron. Goethite, FeO(OH), is 88.85 g/mol: 62.85% iron, and the goethite sheet’s El Paso County analysis gives 62.70%.
The upgrade, worked. One iron atom in siderite becomes one in goethite. A kilogram of siderite, 482 g of iron, becomes 767 g of goethite with the same 482 g. The grade rises by a factor of 1.304 without any iron being added; the carbon dioxide is what goes. That is the direction BGS describes for the North Pennines, where supergene alteration of carbonate ores in the Great Limestone produced workable limonitic ironstones, and where the goethite sheet’s own Occurrence field calls goethite an important component of ore in weathered iron deposits. Goethite itself is on goethite and its magnetism on is goethite magnetic.
Documented failure: the formula is not the grade. BGS gives the Pennine ores up to 40 per cent Fe, Coal Measures clay ironstones a typical iron content of around 25 per cent, and Cumbrian haematite 50 to 60 per cent, against 48.20% for pure siderite, 62.85% for goethite and 69.94% for hematite. Even the richest rock sits below its mineral, because an ore is the mineral plus everything else in the rock. BGS does not say what mineral carries the iron in the Coal Measures clay ironstones, so this page does not assign it. The Cumbrian field is on the West Cumbria hematite mines.
Is siderite a carbonate ore? Cleveland and the ironstones
Siderite is a carbonate, and where it was worked it was worked as a carbonate ore. The IMA formula Fe(CO3) and the sheet’s Calcite group place it with rhodochrosite, magnesite and calcite; BGS calls the Pennine material primary iron carbonate. The BGS Lexicon entry for the Cleveland Ironstone Formation describes the formation as mudstone, siltstone and sandstone with seams of sideritic and berthierine-ooidal ironstone, of Pliensbachian, Lower Jurassic, age. BGS’s Northern England account says the 19th-century discovery of much larger deposits of Jurassic ores in Cleveland, with high-grade haematite from Cumbria, ended the working of the Coal Measures ironstones. Neither source gives Cleveland’s iron grade or its mining dates, so this page gives none.
Roasting. People ask whether siderite is oxidised by roasting. No source fetched for this page describes roasting or smelting siderite, so this page gives no method. The USGS definition says only that ore yields metallic iron when heated in the presence of a reductant.
Telling siderite from the oxides. On their sheets siderite streaks white, goethite brownish yellow to ocher-yellow, hematite cherry-red or reddish brown and magnetite black; the method is on how to use a streak plate. Siderite is also much softer, 3.75–4.25 against 5–6.5 for the oxides. Siderite against ankerite by weight is on the siderite species page. Hazard questions about any mineral are routed to toxic minerals in a collection; nothing here is health or safety advice. Other species are in the species index. Nothing on this site is offered for sale; the wanted list is the only commercial route.