Siderite is a carbonate iron mineral composed primarily of iron carbonate (FeCO₃). Unlike oxide ores such as hematite and magnetite, siderite belongs to the carbonate group and requires additional processing before iron extraction.
It commonly forms in sedimentary environments, hydrothermal veins, and ironstone deposits and is often associated with calcite, quartz, and clay minerals.
Chemical Composition & Crystal Structure
| Component | Percentage (%) |
|---|---|
| Iron (Fe) | ~48.2 |
| Carbonate (CO₃) | ~51.8 |
| Substituting Ions (Mg, Mn, Ca) | 0 – 10 |
| Impurities | Trace – 8 |
Crystal System: Trigonal (Rhombohedral)
Structure Type: Calcite-type
Bonding: Ionic with carbonate groups
Physical Properties
| Property | Typical Value |
|---|---|
| Color | Yellow-brown, gray, greenish, brown |
| Streak | White |
| Density | 3.9 – 4.0 g/cm³ |
| Hardness (Mohs) | 3.5 – 4.5 |
| Crystal Habit | Rhombohedral, massive |
| Magnetic Behavior | Non-magnetic |
Mechanical Properties
| Property | Description |
|---|---|
| Compressive Strength | Low to moderate |
| Tensile Strength | Very low |
| Fracture Behavior | Brittle |
| Wear Resistance | Low |
| Impact Resistance | Poor |
Metallurgical Behavior
During heating, siderite decomposes (calcination):
FeCO₃ → FeO + CO₂ (350–500 °C)
This produces porous iron oxide that can later be reduced similarly to hematite, though with higher fuel consumption due to CO₂ release.
Key Characteristics
✔ Carbonate-based iron ore
✔ Lower iron content than oxides
✔ High loss on ignition (LOI)
✔ Non-magnetic
✔ Easily weathered
Available Forms
| Form | Description |
|---|---|
| Run-of-Mine Ore | Natural carbonate ore |
| Lumps | Low-grade iron feed |
| Fines | Calcination feed |
| Calcined Siderite | Iron oxide intermediate |
| Powder | Chemical and pigment uses |
Applications
Alternative iron source after calcination
Sinter plant blending material
Historical ironmaking
Iron oxide pigments and catalysts
Geological and educational research
Advantages
✔ Widely available in sedimentary basins
✔ Upgradeable through calcination
✔ Porous oxide improves reducibility
✔ Strategic resource in iron-deficient regions
Why Choose Siderite?
Siderite is chosen as a viable alternative iron source where oxide ores are scarce. Although less efficient than hematite or magnetite, its abundance and ability to form porous oxides make it suitable for blending, sintering, and specialty metallurgical applications.