Chalk is a soft, fine-grained, white to light-grey sedimentary limestone composed primarily of calcium carbonate (CaCO₃). It is formed from the accumulation of microscopic marine organisms over millions of years and is valued for its high purity, porosity, and chemical reactivity.
Due to its unique physical and chemical characteristics, chalk is widely used in construction, agriculture, metallurgy, industrial processing, and environmental applications.
Chemical Composition
| Component | Typical Content |
|---|---|
| Calcium Carbonate (CaCO₃) | 90 – 99% |
| Magnesium Carbonate (MgCO₃) | < 1 – 2% |
| Silica (SiO₂) | 0.5 – 5% |
| Alumina (Al₂O₃) | Trace |
| Iron Oxide (Fe₂O₃) | Trace |
| Organic Matter | Minor |
Key Physical Properties
| Property | Typical Value |
|---|---|
| Density | 2.3 – 2.7 g/cm³ |
| Porosity | High (30 – 45%) |
| Color | White to off-white |
| Texture | Soft, powdery |
| Mohs Hardness | ~3 |
| Water Absorption | High |
| Decomposition Temperature | ~825 – 900 °C |
Mechanical Properties
| Property | Description |
|---|---|
| Compressive Strength | Low (2 – 20 MPa) |
| Tensile Strength | Very low |
| Abrasion Resistance | Poor |
| Brittleness | High |
| Elasticity | Negligible |
Chalk is not used as a structural material but excels as a reactive, filler, and flux material.
Metallurgical & Thermal Behavior
On heating, calcium carbonate decomposes:
CaCO₃ → CaO + CO₂
The resulting calcium oxide (quicklime) acts as a flux in metallurgy, removing silica, sulfur, and phosphorus impurities — making chalk essential in steelmaking and non-ferrous metallurgy.
Refining & Processing
Mining:
• Surface quarrying
• Low blasting energy
• Lower environmental impact than hard rock mining
Processing Steps:
• Crushing and grinding
• Classification and drying
• Optional chemical purification
• Surface treatment for coated CaCO₃
Thermal Processing:
• Calcination → Quicklime (CaO)
• Hydration → Slaked Lime (Ca(OH)₂)
Available Forms
✔ Raw chalk stone
✔ Crushed limestone
✔ Ground calcium carbonate (GCC)
✔ Precipitated calcium carbonate (PCC)
✔ Lime (CaO) and slaked lime (Ca(OH)₂)
✔ Powder, granules, pellets, slurry
Applications
Construction & Infrastructure:
• Cement and concrete production
• Road base and lime mortar
Industrial & Chemical:
• Metallurgical flux
• Glass manufacturing
• pH control and neutralization
Agriculture:
• Soil conditioning and acidity control
• Calcium nutrient source
• Animal feed additive
Paper, Plastics & Paints:
• Filler and coating pigment
• Brightness and opacity improvement
Environmental:
• Flue gas desulfurization (FGD)
• Water treatment
• Acid mine drainage control
Advantages of Chalk
✔ Abundant and cost-effective
✔ Easy to mine and process
✔ High calcium carbonate purity
✔ Chemically versatile
✔ Environmentally safer than many minerals
Why Choose Chalk
Chalk is an ideal calcium carbonate source for cement, lime, chemicals, fillers, and metallurgy. Its proven performance, low cost, and wide industrial acceptance make it a critical raw material for construction and industrial infrastructure.