Is siderite magnetic?
Siderite, FeCO3, is not magnetic like magnetite: USGS pulled 17 samples at 0.10 to 0.50 amp. Of 16 anhydrous carbonates, only iron or manganese ones pulled.
Not in the way magnetite is. Siderite, FeCO3, hardness 3.75 to 4.25, has no magnetic property on its Handbook sheet. USGS Open-File Report 99-529 pulled 17 siderite samples at 0.10 to 0.50 amp on a laboratory separator: paramagnetic by its definitions, where magnetite came out at 0.01 amp. Heated siderite can turn into magnetite.
In short
- Paramagnetic, not ferromagnetic. USGS defines ferromagnetic as strongly attracted to a magnet, like a piece of iron, and names magnetite, maghemite, pyrrhotite and pentlandite. Paramagnetic minerals are less magnetic than that, and separable on a laboratory separator at up to 1.70 amp. Siderite, 17 samples, came out at 0.10 to 0.50 amp, best 0.20 to 0.30.
- The iron-or-manganese rule. We matched the anhydrous carbonate rows of USGS Table 1 to the IMA list by script: 16 rows. Five were pulled below the 1.70 amp line, siderite, ankerite, ferrodolomite, rhodochrosite and manganese-bearing calcite, and every one carries iron or manganese. None of the 11 not pulled has either in its formula.
- Documented failure: rhodochrosite. MnCO3 has no iron at all and was pulled at 0.10 to 0.60 amp, across siderite’s whole range. The separator cannot tell the two apart, and USGS names manganese, not just iron, as a cause. Siderite’s own separating figures are on the siderite species page.
- What changes the answer: inclusions and heat. USGS warns that micro-inclusions of magnetite make the lower limit impossible to determine. A 2005 EGU abstract reports nanometre-sized magnetite forming from siderite within minutes at temperatures as low as 300 °C, in the laboratory. Worked, 20.00 g of siderite holds 9.64 g of iron, enough for at most 13.32 g of magnetite.
- Without a magnet, the streak plate separates the iron minerals. On their Handbook sheets siderite streaks white, magnetite black and hematite cherry-red to reddish brown. The full magnet question across the site’s species is on which minerals are magnetic.
| Mineral (USGS name) | IMA formula | Fe or Mn in the formula | Iron by mass, worked | USGS total range (amp) | USGS best range (amp) | Samples | Pulled below 1.70 amp? |
|---|---|---|---|---|---|---|---|
| Siderite | Fe(CO3) | Fe | 48.20% | 0.10 to 0.50 | 0.20 to 0.30 | 17 | Yes |
| Rhodochrosite | Mn(CO3) | Mn | 0% (47.79% Mn) | 0.10 to 0.60 | 0.20 to 0.40 | 5 | Yes |
| Ankerite | CaFe2+(CO3)2 | Fe | 25.86% | 0.30 to 0.70 | 0.40 to 0.50 | 1 | Yes |
| Ferrodolomite | No IMA row (USGS also writes dolomite-(Fe)) | Fe, by name | Not worked | 0.20 to 1.30 | 0.40 to 1.10, depends on chemistry | 8 | Yes |
| Calcite-(Mn) | No IMA row | Mn, by name | Not worked | 0.50 to 1.70 | 0.90 to 1.10 | 1 | Yes |
| Dolomite | CaMg(CO3)2 | Neither | 0% | Above 1.70 | Above 1.70 | 4 | No |
| Calcite | Ca(CO3) | Neither | 0% | Above 1.70 | Above 1.70 | 8 | No |
| Magnesite | Mg(CO3) | Neither | 0% | Above 1.70 | Above 1.70 | 2 | No |
| Smithsonite | Zn(CO3) | Neither | 0% | Above 1.70 | Above 1.70 | 3 | No |
| Aragonite | Ca(CO3) | Neither | 0% | Above 1.70 | Above 1.70 | 2 | No |
| Cerussite | Pb(CO3) | Neither | 0% | Above 1.70 | Above 1.70 | 3 | No |
| Strontianite | Sr(CO3) | Neither | 0% | Above 1.70 | Above 1.70 | 1 | No |
| Witherite | Ba(CO3) | Neither | 0% | Above 1.70 | Above 1.70 | 1 | No |
| Bismutite | Bi2O2(CO3) | Neither | 0% | Above 1.70 | Above 1.70 | 3 | No |
| Nahcolite | NaH(CO3) | Neither | 0% | Above 1.70 | Above 1.70 | 2 | No |
| Shortite | Na2Ca2(CO3)3 | Neither | 0% | Above 1.70 | Above 1.70 | 2 | No |
| Magnetite, for scale (not counted) | Fe2+Fe3+2O4 | Fe | 72.36% | Below 0.01 to 0.05 | 0.01 | 6 | Ferromagnetic |
Is siderite magnetic? What the sheet and the separator record
Siderite is paramagnetic on a laboratory separator and has no magnetic property on its reference sheet. The Handbook of Mineralogy siderite sheet gives Fe2+CO3, hexagonal, hardness 3.75 to 4.25, measured density 3.96, perfect rhombohedral cleavage and a white streak, and is silent on magnetism. Silence is absence from the source, not a measured zero.
The measurement. USGS Open-File Report 99-529, Magnetic Susceptibilities of Minerals (Rosenblum and Brownfield) passed dry 125 to 150 µm grains through a Frantz isodynamic separator at a 15 degree side tilt. Siderite, 17 samples, was extracted at 0.10 to 0.50 amp, best 0.20 to 0.30. By the report’s definitions that is paramagnetic: separable at up to 1.70 amp, the greatest value reached on the machine. Ferromagnetic minerals are a separate class, strongly attracted to a magnet like a piece of iron: magnetite, maghemite, pyrrhotite and pentlandite. Magnetite’s best range was 0.01 amp.
The boundary. Siderite is not ferromagnetic, and neither source tests a hand magnet, so this page does not predict what one will do. It is 48.20% iron by mass, worked, and magnetite 72.36%, but iron content alone is not the answer: the site’s which minerals are magnetic page shows hematite, 69.94% iron, with no magnetic entry on its sheet.
Why siderite is pulled and calcite is not: the iron-or-manganese rule
Every carbonate that USGS pulled below 1.70 amp carries iron or manganese. Method: each row of Table 1 was matched by name to the September 2026 IMA-CNMNC list of minerals (September 2026) (pdftotext -layout, both); rows whose IMA formula contains CO3 and no hydroxyl, water, halogen or other anion group were kept, with the two USGS-only carbonate names, ferrodolomite and calcite-(Mn). An independent line-by-line scan found the same 14 IMA-named carbonates. That gives 16 rows. Five were pulled below 1.70 amp: siderite, ankerite, ferrodolomite, rhodochrosite and calcite-(Mn). The other 11, from calcite and dolomite to witherite, were not, and none has iron or manganese in its formula.
USGS draws the same conclusion. Its report says iron substituting for calcium or magnesium is the best example of a metal changing susceptibility, and that iron-bearing carbonates are more magnetic than other species that are iron-free. In the table, siderite, 48.20% iron, has a best range of 0.20 to 0.30 amp; ankerite, CaFe2+(CO3)2 on the IMA list, 25.86% iron worked, 0.40 to 0.50; dolomite, with none, was not pulled. Among these 16 rows siderite has the most samples, 17, and its best range starts at the lowest current, 0.20, which it shares with rhodochrosite.
Documented failure: rhodochrosite. MnCO3, with no iron, came out at 0.10 to 0.60 amp, overlapping all of siderite’s range. In its general discussion the report says that, other than iron, only manganese and copper have been noted to bring minerals into the paramagnetic range. A separator says “iron or manganese carbonate”, not “siderite”. The rule is a description of these 16 rows; hydrated and copper carbonates such as malachite were left out by the method and behave differently. Rhodochrosite’s own separator page is is rhodochrosite magnetic.
My siderite pulls a magnet: what changes the answer
Magnetite inside it. USGS notes that when micro-inclusions of magnetite or other ferromagnetic minerals are present, it is difficult or impossible to determine a mineral’s actual lower limit of extraction. A siderite specimen that responds to a hand magnet is reporting something other than siderite’s own paramagnetism; the way to localise that is set out on is tetrahedrite magnetic and is not repeated here; a non-iron case is on is stibnite magnetic.
Heat. Two conference abstracts describe siderite becoming magnetic on heating, as a laboratory result. Isambert and others, EGU 2005 abstract reports that natural manganese-bearing siderite heated in air breaks down into Mn-hematite and Mn-magnetite, and that nanometre-sized magnetite can form from siderite within minutes at temperatures as low as 300 °C. Fukuchi, JpGU 2013 abstract says siderite can produce magnetite or maghemite via wüstite by thermal decomposition, with products that vary with oxygen and temperature. Neither is a home method, and this page gives none.
The iron budget, worked. On standard atomic weights FeCO3 is 115.85 and Fe3O4 231.53. A 20.00 g piece of siderite holds 9.64 g of iron; if every atom ended up as magnetite, that is 13.32 g of magnetite, 66.6% of the starting mass. That is an upper bound from the formulas, not a yield measured by either abstract. The identification guides are indexed at the collecting guides. Nothing on this site is offered for sale; the wanted list is the only commercial route.
Siderite, magnetite or hematite? Telling them apart without a magnet
Streak separates all three. On their Handbook sheets siderite’s streak is white, magnetite’s black and hematite’s cherry-red or reddish brown. The method is on how to use a streak plate.
Weight separates siderite from the oxides. A 20.00 g piece weighs 14.95 g in water as siderite (3.96), 16.14 g as magnetite and 16.20 g as hematite, the figures on the live species pages. Siderite is at least 1.19 g lighter; magnetite and hematite are 0.06 g apart and need the streak. The method is on how to measure specific gravity at home.
Habit helps. Siderite’s sheet gives rhombohedral to scalenohedral crystals with perfect rhombohedral cleavage; magnetite’s gives octahedra. The magnet question for a grey sulphide is on is galena magnetic.