Is Magnesium Carbonate Soluble in Water? Solubility Facts & Comparisons

Wondering if magnesium carbonate is soluble in water? It’s practically insoluble—learn the real solubility data, why it matters in industry, and how it compares to magnesium hydroxide and oxide.

I’ve been working with magnesium compounds for years in the chemical industry.

Clients often ask me about solubility when selecting products.

Today, let’s tackle a common one: is magnesium carbonate soluble in water?

You’re probably here because you’re sourcing materials.

Or troubleshooting a formulation.

Or just curious about how these compounds behave.

Straight answer: No, magnesium carbonate is not meaningfully soluble in water.

It’s considered practically insoluble.

Most sources list it at around 0.02 g per 100 g of water at room temperature.

That’s sparingly soluble at best.

In practice, it doesn’t dissolve much.

Why Magnesium Carbonate Has Low Solubility in Water

Solubility comes down to lattice energy versus hydration energy.

Magnesium carbonate (MgCO₃) is an ionic compound.

The lattice energy—the force holding the Mg²⁺ and CO₃²⁻ ions together—is high.

Water molecules can’t pull those ions apart easily.

Compare that to more soluble salts like magnesium chloride.

The chloride ions hydrate better.

For carbonates of group 2 metals, solubility decreases down the group.

But magnesium carbonate sits on the low end anyway.

Its Ksp (solubility product constant) is around 3.5 × 10⁻⁸.

That confirms very low dissolution.

In pure water, molar solubility is roughly 2 × 10⁻⁴ M.

Tiny amount.

Factors That Affect Solubility Slightly

• Temperature: Increases a bit with heat, but still low.
• CO₂ presence: In carbonated water, it can form more soluble bicarbonate temporarily.
• pH: Acidic conditions dissolve it fast—effervescence with CO₂ release.

But in neutral water? Forget significant solubility.

How Magnesium Carbonate Compares to Related Compounds

We often get asked about magnesium oxide and hydroxide too.

Here’s a quick breakdown:

• Magnesium carbonate (MgCO₃): Practically insoluble in water.
• Magnesium hydroxide (Mg(OH)₂): Even less soluble—known as “milk of magnesia” suspension because it doesn’t dissolve well.
• Magnesium oxide (MgO): Reacts slowly with water to form hydroxide, but the oxide itself is insoluble. Highly reactive when calcined properly.

All three are low-solubility in water.

That’s why they’re great for applications needing stability.

Like flame retardants, antacids, or fillers.

A few years back, I was chatting with a formulator friend over coffee.

He was trying to make a water-based suspension with magnesium carbonate.

Kept shaking it, but it settled out fast.

I told him: “That’s because it’s insoluble—switch to a slurry process or use a dispersant.”

He did, and it worked perfectly for his rubber compound.

Real-world reminder that knowing solubility saves headaches.

Practical Implications in Industry

Low water solubility is often a feature, not a bug.

• Keeps it stable in humid environments.
• Prevents caking in powders (think gym chalk).
• Ideal for controlled release in pharma or agriculture.

But if you need solubility?

Go for magnesium sulfate or chloride instead.

Or dissolve carbonate in acid first.

Frequently Asked Questions

Is magnesium carbonate completely insoluble in water? No, it’s sparingly soluble—about 0.02 g/100 g water. Practically insoluble for most uses.

Why does magnesium carbonate fizz in acid but not water? In acid, it reacts to form soluble magnesium salts, water, and CO₂ gas. No reaction in neutral water.

Can I use magnesium carbonate in water treatment? Not for dissolving magnesium ions. Better for pH adjustment or as a precipitant. Magnesium hydroxide is more common there.

What’s the difference in solubility between light and heavy magnesium carbonate? Both forms are insoluble in water. “Light” is fluffier, “heavy” denser—but solubility is similar.

Does temperature make magnesium carbonate soluble? It increases slightly, but still remains very low. Not enough for most practical dissolution.

In the end, understanding is magnesium carbonate soluble in water helps you pick the right grade for your process.

It’s a reliable, low-solubility workhorse in our industry.