Description

Calcium carbonate (chemical formula CaCO₃) is a common chemical compound found widely in nature. Here’s a clear, quick overview:

What it is

A white, odorless powder or crystalline solid.

Occurs naturally in limestone, marble, chalk, coral, and shells.

Common uses

Antacid (reduces stomach acid)

Calcium supplement

Building materials (cement, lime, marble)

Industrial uses (plastics, paints, paper fillers)

Agriculture (soil pH adjustment—agricultural lime)

Key properties

Insoluble in water

Reacts with acids to produce carbon dioxide (the fizz when acid hits limestone)

Molar mass: 100.09 g/mol

Decomposes when heated → CaO (lime) + CO₂

Where it’s found in biology

Component of bones, teeth, shells of marine animals, egg shells.

Calcium Carbonate — Detailed Chemical Profile
1. Chemical Identity

IUPAC name: Calcium trioxocarbonate

Chemical formula: CaCO₃

Molar mass: 100.0869 g/mol

CAS number: 471-34-1

EC number: 207-439-9

2. Structure & Bonding

Composed of a Ca²⁺ cation and CO₃²⁻ carbonate anion.

Carbonate ion geometry: trigonal planar.

Bonding within CO₃²⁻: resonance-stabilized, bond order ~1.33.

Solid exists mainly in ionic lattice structures with strong electrostatic interactions.

3. Polymorphs (Crystal Forms)

Calcium carbonate has three anhydrous polymorphs:

1. Calcite

Most stable polymorph at ambient conditions.

Crystal system: Trigonal (rhombohedral)

Density: ~2.71 g/cm³

Common in limestone, marble.

2. Aragonite

Metastable, forms in marine biological systems.

Crystal system: Orthorhombic

Density: ~2.93 g/cm³

Converts to calcite over geological timescales.

3. Vaterite

Least stable and rare.

Crystal system: Hexagonal

Density: ~2.54 g/cm³

Hydrated forms: monohydrocalcite (CaCO₃·H₂O) and ikaite (CaCO₃·6H₂O) occur in cold environments.

4. Physical Properties
Property Value
Appearance White powder or colorless crystals
Odor Odorless
Density 2.54–2.93 g/cm³ (polymorph dependent)
Melting point Decomposes before melting
Thermal decomposition ~825°C → CaO + CO₂
Solubility in water Very low (≈ 0.013 g/L at 25°C)
Solubility behavior Solubility increases in the presence of CO₂ (forms bicarbonate)
Hardness (Mohs) Calcite: 3
5. Chemical Properties
Reactivity

With acids:
CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂↑

With CO₂ and water: forms calcium bicarbonate
CaCO₃ + CO₂ + H₂O ↔ Ca(HCO₃)₂

With strong heat: thermal decomposition
CaCO₃ → CaO + CO₂

With ammonium salts: liberation of CO₂.

pH Behavior

Nearly neutral in water due to low solubility.

Acts as a buffer in natural waters, maintaining alkalinity.

6. Natural Occurrence

Found abundantly as:

Limestone, chalk, marble

Marine shells, corals, exoskeletons

Stalactites/stalagmites (calcite)

Geological formations shaped by sedimentation and biomineralization.

7. Industrial Production
Limestone mining and processing

Crushed, ground, and purified from natural sources.

PCC (Precipitated Calcium Carbonate)

Produced via:

Calcination: CaCO₃ → CaO + CO₂

Hydration: CaO + H₂O → Ca(OH)₂

Carbonation: Ca(OH)₂ + CO₂ → CaCO₃↓ (precipitate)

Allows control of particle size, morphology, and purity.

8. Applications (Technical)

Fillers: plastics, rubber, paper, paints

Cement & concrete industry

Pharmaceuticals: antacids, tablet excipients

Food additive: E170

Agriculture: soil pH adjustment, animal feed

Water treatment: neutralizes acids, remineralizes RO water

9. Safety & Handling

Generally recognized as safe (GRAS), low toxicity.

Dust may cause:

mild respiratory irritation

eye irritation

Avoid inhalation; use dust protection in industrial conte