Qual é a fórmula do carbonato de magnésio? MgCO₃ Explained Clearly

What is the formula of magnesium carbonate? It’s Mgco₃ — the standard anhydrous form. Learn about variations like hydrated and basic types, plus common uses in industry and sports.

I’ve fielded the question what is the formula of magnesium carbonate from clients, students, and formulators more times than I can remember.

Most people expect a single clean answer.

The core, anhydrous compound is indeed Mgco₃.

That’s the formula you’ll see in textbooks, PubChem, and basic specs.

But in real-world supply and applications, things get a little more nuanced.

Commercial “Carbonato de magnésio” is often a hydrated or basic form.

Let’s break it down plainly so you know exactly what you’re dealing with.

The Standard Chemical Formula: Mgco₃

Mgco₃ is the simplest and most fundamental formula.

• Mg— magnesium cation (Mg²⁺)
• CO₃— carbonate anion (CO₃²⁻)

One magnesium balances one carbonate.

Molecular weight: ≈84.31 g/mol

This is the anhydrous form, known mineralogically as magnesite.

It’s a white, crystalline solid with a calcite-like structure.

Common Commercial Variations and Their Formulas

When people buy “Carbonato de magnésio” for pharma, comida, borracha, or gym chalk, they usually get one of these:

• Light magnesium carbonate— often approximated as basic hydrated forms like (Mgco₃)₄·Mg(OH)₂·4H₂O or similar. Very fluffy, low density.
• Heavy magnesium carbonate— denser, frequently (Mgco₃)₃·Mg(OH)₂·3H₂O or tetrahydrate versions. More compact.

These are basic magnesium carbonates (also called magnesium hydroxide carbonate).

Typical formulas you’ll see in specs:

• Light: roughly (Mgco₃)₃·Mg(OH)₂·3H₂O
• Heavy: roughly (Mgco₃)₃·Mg(OH)₂·4H₂O or Mg₅(CO₃)₄(OH)₂·4H₂O (hydromagnesite-like)

They contain both carbonate and hydroxide groups, plus water.

That’s why the MgO content is often listed as 40–45% instead of the ~47% for pure MgCO₃.

Why the Formula Matters in Applications

The exact composition affects performance.

• Giz de ginástica / giz de escalada— almost always light, fluffy basic magnesium carbonate. High surface area for sweat absorption.
• Rubber and plastics filler— heavier, denser grades for better loading and reinforcement.
• Pharma antacids— basic hydrated forms for controlled acid neutralization.
• Precursor to MgO— calcined (heated) to drive off CO₂ and H₂O, regardless of starting hydration.

A rubber compounder I know once ordered “Carbonato de magnésio” without specifying light or heavy.

Got the light fluffy version instead of the dense one he needed.

Mixing time doubled, dispersion was poor, and batch scrapped.

Specifying “heavy magnesium carbonate” fixed it next run.

Small detail, big cost.

Quick Reference: Magnesium Carbonate Formulas at a Glance

Perguntas frequentes

What is the simplest formula of magnesium carbonate? Mgco₃ — that’s the anhydrous, theoretical form (magnesite).

Is gym chalk really MgCO₃? Sim, but usually a light basic hydrated version — not pure anhydrous MgCO₃.

Why do specs list magnesium carbonate as having 40–45% MgO? Commercial products are basic/hydrated forms. Pure MgCO₃ would be ~47% MgO.

What’s the difference in formula between light and heavy magnesium carbonate? Both are basic hydrated carbonates, but light versions have slightly less water or different crystal habits, leading to lower bulk density.

Can magnesium carbonate be anhydrous in products? Rarely. Most supplied material includes hydration or basic character for stability and handling.

So when someone asks what is the formula of magnesium carbonate, start with Mgco₃ — then clarify whether they mean the pure anhydrous or the common commercial basic/hydrated types.

It’s a small distinction that saves a lot of troubleshooting downstream.