Identification guide · Carbonates
How to Identify Magnesite
Magnesite is usually white, gray, and yellowish with a vitreous luster and is translucent. It has a Mohs hardness of 4. A steel knife blade (Mohs 5.5) scratches it; a copper coin does not. Its streak is white. It is most often confused with Dolomite, Siderite, and Calcite; the tests below separate them.
Magnesite identification checklist
| Color | White, Gray, Yellowish, Brown, Colorless | Look at a clean, dry surface in daylight. Color zoning, banding or spots are as diagnostic as the hue. |
|---|---|---|
| Luster | Vitreous | Fresh surfaces shine like glass; a dull surface usually means weathering, so chip or wet a corner. |
| Transparency | Translucent | Hold a thin edge up to a bright light and note whether light passes through. |
| Mohs hardness | 4 | A steel knife blade (Mohs 5.5) scratches it; a copper coin does not. |
| Streak | White | Drag a corner across unglazed porcelain (the back of a bathroom tile) and check the powder color. |
| Cleavage | Perfect rhombohedral | |
| Fracture | Conchoidal to uneven | Broken surfaces show smooth, curved, shell-like scoops. |
| Specific gravity | 3 | Ordinary rock-like heft (specific gravity about 3), similar to quartz. |
| Crystal system | Trigonal |
Extra tests for Magnesite
Acid test. Fizzes only weakly in vinegar or dilute acid unless powdered first.
Glass check. Magnesite shares a glassy luster and conchoidal fracture with man-made glass. Glass sits near Mohs 5.5 and often contains round gas bubbles, so a hardness test and a hand lens separate them.
Magnesite look-alikes and how to tell them apart
Both sit near Mohs 4, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Magnesite vs Dolomite →
Both sit near Mohs 4, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Magnesite vs Siderite →
Magnesite is harder (Mohs 4) than Calcite (Mohs 3), so Magnesite will scratch Calcite and not the other way round. A copper coin (Mohs 3.5) scratches it, but a fingernail does not. Magnesite vs Calcite →
Quartz is harder (Mohs 7) than Magnesite (Mohs 4), so Quartz will scratch Magnesite and not the other way round. A steel knife blade (Mohs 5.5) scratches it; a copper coin does not.
Field tips
- Look for white to gray crystalline or porcelain-like masses with perfect rhombohedral cleavage in crystalline material.
- Magnesite effervesces only in warm acid, which separates it from readily fizzing calcite.
- Distinguish it from dolomite by chemical testing and from calcite by its higher hardness and weaker acid reaction.
Magnesite identification FAQ
How can you tell if a rock is Magnesite?
Check the color (white, gray, yellowish, and brown), the vitreous luster, a Mohs hardness of 4 and a white streak. Photographing it with the StoneSnap app gives a match in seconds.
What is the hardness of Magnesite?
Magnesite has a Mohs hardness of 4. A steel knife blade (Mohs 5.5) scratches it; a copper coin does not.
What is the difference between Magnesite and Dolomite?
Magnesite (Mohs 4, vitreous luster) and Dolomite (Mohs 3.5–4, vitreous to dull luster) look alike, but hardness, streak and heft usually separate them. See the full Magnesite vs Dolomite comparison for a side-by-side table.
Is Magnesite worth anything?
Entry-level Magnesite specimens sell for around $3, typical collector pieces about $25, and premium examples $150 or more depending on size, quality and locality.
What color is Magnesite?
Magnesite is most often white, gray, yellowish, and brown. Color varies with impurities and locality, so confirm with hardness and luster rather than color alone.
