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Magnesium oxide

Magnesium oxide suppliers and sourcing guide

Magnesium oxide is made by heating magnesium hydroxide or magnesium carbonate, and it occurs naturally as the mineral periclase. Moderate heat gives a bulky light grade and more intense heating gives a dense heavy grade; the magnesium hydroxide feed is often precipitated from seawater or brine, while carbonate feed is often mined magnesite. With roughly 60% magnesium it is the most concentrated common magnesium source, bought as powder or granules for tablets and capsules.

See suppliersWhat to ask for on the COA
Also known as
MgO · Magnesia · E530 · Calcined magnesia
Facts checked
November 2026

Forms and grades of magnesium oxide

Suppliers sell different products under the same name. Specify the one you need.

  • Light magnesium oxide

    Bulky, low-density powder made at lower calcining temperatures; reacts more readily and fills more capsule volume per gram.

  • Heavy magnesium oxide

    Dense powder made at high temperature, preferred where capsule or tablet size is limited.

  • Directly compressible granules

    Granulated grades, sometimes with a binder, for tablet presses.

  • Seawater or brine-derived

    Made from magnesium hydroxide precipitated from seawater or brine, often marketed as marine magnesium.

  • Mined-magnesite grades

    Made by calcining mined magnesium carbonate; impurity profile depends on the ore.

What to check on the COA

Compare each result with your own specification when the lot arrives.

Assay
Magnesium oxide content on the ignited basis by EDTA titration, against a USP or Food Chemicals Codex specification.
Loss on ignition
Water and carbon dioxide picked up from the air, which rises as the oxide ages and converts partly to hydroxide and carbonate.
Calcium oxide and acid-insoluble substances
Limits on calcium and insoluble mineral matter from the raw material.
Lead, arsenic and other metals
Heavy metals by ICP-MS, which vary with ore or brine source.
Bulk density and particle size
Tapped density distinguishes light from heavy grades and sets capsule fill weight.

Storage, lots and expiry

Storage and shelf life

Magnesium oxide slowly absorbs water and carbon dioxide from air, so keep it in tightly closed containers in a dry area and reseal opened bags. Do not store it next to acids. Shelf life is set by the supplier's specification; retest loss on ignition and assay on older stock.

Lots and expiry dates

Record the grade (light or heavy), bulk density, assay and loss on ignition for each lot. A density change between lots alters capsule fill weight, so check it before running encapsulation.

Regulatory status

Facts from regulators and standards bodies, each linked to its source.

This is general information, not regulatory advice. Status differs by country and by how the ingredient is used, so check the rules for your product and market.

Magnesium oxide suppliers

Manufacturers and distributors whose own websites say they sell it.

We are checking magnesium oxide suppliers now

Every listing is checked against the supplier’s own website before it goes live, so this list fills in over the coming weeks. The specs and COA checklist above are ready today.

Sell magnesium oxide? Request a listing

Frequently asked questions

What forms of magnesium oxide can brands buy?

Common forms include light magnesium oxide, heavy magnesium oxide, directly compressible granules, seawater or brine-derived and mined-magnesite grades. Ask each supplier for the specification sheet of the exact grade they quote.

What should the COA for magnesium oxide include?

Expect assay, loss on ignition, calcium oxide and acid-insoluble substances, lead, arsenic and other metals and bulk density and particle size, each with its method, specification and result for that lot.

How should magnesium oxide be stored?

Magnesium oxide slowly absorbs water and carbon dioxide from air, so keep it in tightly closed containers in a dry area and reseal opened bags. Do not store it next to acids. Shelf life is set by the supplier's specification; retest loss on ignition and assay on older stock.

What is the regulatory status of magnesium oxide?

21 CFR 184.1431 affirms magnesium oxide as GRAS, describes light and heavy grades, and allows its use in infant formula. Health Canada's List of Permitted Anticaking Agents includes magnesium oxide for unstandardized dry mixes, except those used in preparations of meat and meat by-products. Health Canada's Multi-Vitamin/Mineral Supplements monograph for natural health products lists magnesium oxide among the source ingredients for magnesium (Table 2).

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