Identification guide · Silicate Minerals
How to Identify Prehnite
Prehnite is usually green, yellow-green, and yellow with a vitreous luster and is translucent. It has a Mohs hardness of 6.25. 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 Jadeite, Microcline, and Nepheline; the tests below separate them.
Prehnite identification checklist
| Color | Green, Yellow-green, Yellow, White, 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 | Translucent | Hold a thin edge up to a bright light and note whether light passes through. |
| Mohs hardness | 6.25 | 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 | Good | |
| Fracture | Uneven | |
| Specific gravity | 2.88 | Ordinary rock-like heft (specific gravity about 2.88), similar to quartz. |
| Crystal system | Orthorhombic |
Prehnite look-alikes and how to tell them apart
Both sit near Mohs 6.25, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Prehnite vs Jadeite →
Both sit near Mohs 6.25, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Prehnite vs Microcline →
Both sit near Mohs 6.25, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Prehnite vs Nepheline →
Both sit near Mohs 6.25, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
Field tips
- Look for soft green to yellow-green color and rounded, botryoidal aggregates lining rock cavities.
- Prehnite is moderately hard, translucent, and has a glassy luster on crystal surfaces.
- It commonly occurs in basalt with zeolites, calcite, and epidote, which helps confirm identification.
Prehnite identification FAQ
How can you tell if a rock is Prehnite?
Check the color (green, yellow-green, yellow, and white), the vitreous luster, a Mohs hardness of 6.25 and a white streak. Photographing it with the StoneSnap app gives a match in seconds.
What is the hardness of Prehnite?
Prehnite has a Mohs hardness of 6.25. 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 Prehnite and Jadeite?
Prehnite (Mohs 6.25, vitreous luster) and Jadeite (Mohs 6.75, vitreous luster) look alike, but hardness, streak and heft usually separate them. See the full Prehnite vs Jadeite comparison for a side-by-side table.
Is Prehnite worth anything?
Entry-level Prehnite specimens sell for around $10, typical collector pieces about $70, and premium examples $400 or more depending on size, quality and locality.
What color is Prehnite?
Prehnite is most often green, yellow-green, yellow, and white. Color varies with impurities and locality, so confirm with hardness and luster rather than color alone.
