Less known facts about: Calcium Carbonate

This article is part of the “Less Known Facts About Excipients” series by Philippe Tschopp.

Calcium Carbonate: A Widely used inorganic compound in pharmaceutical formulations

Calcium carbonate is one of the most abundant minerals on Earth. While it is widely recognised as a calcium supplement and antacid, it is also an important pharmaceutical excipient used in tablets, capsules and powder formulations.

Although naturally occurring calcium carbonate has been used for centuries, modern pharmaceutical formulations increasingly rely on highly purified grades manufactured under tightly controlled conditions to ensure consistent quality and performance.

Calcium carbonate (CaCO₃) occurs naturally in limestone, chalk, marble and marine shells. Pharmaceutical-grade calcium carbonate may be obtained either by purifying naturally mined deposits or by synthetic precipitation, resulting in materials with different particle characteristics and pharmaceutical functionalities.¹–³

How is pharmaceutical calcium carbonate produced?

Two manufacturing routes are commonly used.

Route 1: Ground Calcium Carbonate (GCC)

1. Mining High-purity limestone or marble deposits are carefully selected and extracted.
2. Crushing and Milling The mineral is crushed and milled to the desired particle size distribution.
3. Classification Air classification or sieving produces grades with controlled particle size and morphology.
4. Purification Additional processing removes impurities to comply with pharmacopeial specifications.¹–⁴

Route 2: Precipitated Calcium Carbonate (PCC)

1. Calcination Limestone is heated to produce calcium oxide (quicklime).
2. Hydration Calcium oxide reacts with water to form calcium hydroxide.
3. Carbonation Carbon dioxide is introduced, precipitating highly pure calcium carbonate crystals.
4. Drying and Milling The precipitated material is filtered, dried and milled to obtain pharmaceutical-grade powders with tightly controlled particle size and morphology.¹–⁵

What makes calcium carbonate unique?

Although the chemical composition is identical, ground calcium carbonate (GCC) and precipitated calcium carbonate (PCC) can exhibit significantly different pharmaceutical properties because of their particle size, crystal morphology and specific surface area.

Its most valuable characteristics include:

• High chemical purity
• Excellent compressibility (depending on grade)
• High whiteness
• Good flow properties
• pH buffering capacity
• High calcium content (approximately 40% elemental calcium)

These properties make calcium carbonate suitable for both therapeutic and excipient functions.

Pharmaceutical applications

Pharmaceutical-grade calcium carbonate is used in:

• Tablet fillers
• Direct compression formulations
• Calcium supplements
• Antacid tablets
• Powder formulations
• Nutraceutical products
• Chewable tablets¹,²

Its primary functions include:

• Diluent (filler)
• Calcium source
• Antacid
• pH modifier
• Compression aid

Considerations for formulators

The selection of calcium carbonate depends strongly on particle engineering. Precipitated grades generally offer greater control over particle morphology and compressibility, while ground grades are often selected for their cost-effectiveness and high purity.

Because calcium carbonate reacts readily with acids, formulators should carefully evaluate compatibility with acid-sensitive active ingredients and formulations requiring acidic microenvironments.¹–⁴

Major pharmaceutical manufacturers

Examples of established manufacturers and suppliers include:

• Omya AG
• Dr. Paul Lohmann
• Magnesia
• Imerys
• Minerals Technologies Inc. (Specialty Minerals® PCC)
• Huber Engineered Materials
• Calcinor S.A.

Did you know?

Marine organisms such as corals, oysters and microscopic plankton continuously produce calcium carbonate to build shells and skeletons. Over millions of years, these biological structures have contributed to the formation of many of today’s limestone deposits, meaning some pharmaceutical calcium carbonate ultimately originates from ancient marine ecosystems.

At the same time, synthetic precipitated calcium carbonate (PCC) demonstrates how modern manufacturing can reproduce nature’s chemistry while offering far greater control over particle size and functionality.

By Philippe Tschopp
Philippe Tschopp writes about pharmaceutical excipients, formulation and oral drug delivery, with a focus on excipient functionality, practical formulation considerations and lesser-known material properties.

Sources

1. Rowe RC, Sheskey PJ, Quinn ME (Eds.). Handbook of Pharmaceutical Excipients. Pharmaceutical Press / American Pharmacists Association.
2. European Pharmacopoeia (Ph. Eur.). Monograph: Calcium Carbonate.
3. United States Pharmacopeia–National Formulary (USP–NF). Monograph: Calcium Carbonate.
4. Omya AG. Pharmaceutical Calcium Carbonate Technical Documentation.
5. Minerals Technologies Inc. Specialty Minerals®. Technical literature for Precipitated Calcium Carbonate (PCC).
6. Imerys. Pharmaceutical Mineral Solutions and Calcium Carbonate Product Information.
7. Greenwood NN, Earnshaw A. Chemistry of the Elements. Chapter on alkaline earth carbonates.
8. Source newsletter: Philippe Tschopp, “Less Known Facts About Excipients #6: Calcium Carbonate | LinkedIn, newsletter,2026. https://www.linkedin.com/pulse/less-known-facts-excipients-6-calcium-carbonate-philippe-tschopp-iqhoe/

Disclaimer

This article is based on publicly available information and industry sources at the time of writing and supported by AI. While every effort has been made to ensure accuracy, completeness, and fair representation, the author does not guarantee that all information is current, error-free, or reflective of the latest developments.

The content is provided for informational and educational purposes only and does not constitute technical, regulatory, or commercial advice. No liability is accepted for decisions made based on this material. Readers are encouraged to consult the original manufacturers and official sources to verify details before making professional or business decisions.

Read also the other article from the series “Less known facts about…” here:

• Shellac – coming soon
• Pullulan- coming soon
• Carnauba Wax- coming soon
• Gum Arabic – coming soon