Identification guide · Silicate Minerals
How to Identify Natrolite
Natrolite is usually colorless, white, and pink with a vitreous luster and is transparent. It has a Mohs hardness of 5.5. It is about as hard as window glass: a knife barely marks it, while a steel file (Mohs 6.5) will. Its streak is white. It is most often confused with Analcime, Apophyllite, and Calcite; the tests below separate them.
Natrolite identification checklist
| Color | Colorless, White, Pink, Yellow, Gray | 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 | Transparent | Hold a thin edge up to a bright light and note whether light passes through. |
| Mohs hardness | 5.5 | It is about as hard as window glass: a knife barely marks it, while a steel file (Mohs 6.5) will. |
| Streak | White | Drag a corner across unglazed porcelain (the back of a bathroom tile) and check the powder color. |
| Cleavage | Perfect on {110} | |
| Fracture | Uneven | |
| Specific gravity | 2.25 | Noticeably light in the hand for its size (specific gravity about 2.25). |
| Crystal system | Orthorhombic |
Natrolite look-alikes and how to tell them apart
Both sit near Mohs 5.5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Natrolite vs Analcime →
Both sit near Mohs 5.5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Natrolite vs Apophyllite →
Natrolite is harder (Mohs 5.5) than Calcite (Mohs 3), so Natrolite will scratch Calcite and not the other way round. A copper coin (Mohs 3.5) scratches it, but a fingernail does not. Natrolite vs Calcite →
Both sit near Mohs 5.5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Natrolite vs Scapolite →
Field tips
- Look for slender, needle-like white or colorless crystals, often in radiating sprays in basalt cavities.
- Natrolite is moderately soft at about 5 to 5.5 and has a low density and perfect prismatic cleavage.
- It fuses readily in a flame, helping separate it from harder silicates with similar habits.
Natrolite identification FAQ
How can you tell if a rock is Natrolite?
Check the color (colorless, white, pink, and yellow), the vitreous luster, a Mohs hardness of 5.5 and a white streak. Photographing it with the StoneSnap app gives a match in seconds.
What is the hardness of Natrolite?
Natrolite has a Mohs hardness of 5.5. It is about as hard as window glass: a knife barely marks it, while a steel file (Mohs 6.5) will.
What is the difference between Natrolite and Analcime?
Natrolite (Mohs 5.5, vitreous luster) and Analcime (Mohs 5–5.5, vitreous luster) look alike, but hardness, streak and heft usually separate them. See the full Natrolite vs Analcime comparison for a side-by-side table.
Is Natrolite worth anything?
Entry-level Natrolite specimens sell for around $8, typical collector pieces about $45, and premium examples $250 or more depending on size, quality and locality.
What color is Natrolite?
Natrolite is most often colorless, white, pink, and yellow. Color varies with impurities and locality, so confirm with hardness and luster rather than color alone.
