Identification guide · Igneous Rocks
How to Identify Pumice
Pumice is unmistakable in hand specimen thanks to its extremely low density, pale gray, tan, or white color, and its sponge-like network of tiny, elongated vesicles, giving it a rough, abrasive feel and a dull, glassy luster where the bubble walls are thin. It streaks white and has a hardness around 5 to 6, though the whole rock crumbles easily because of its fragile, porous structure rather than any inherent softness in the glass itself. Its main look-alike, scoria, is denser, darker, and sinks in water, while pumice's ability to float is the simplest and most reliable field test available.
Pumice identification checklist
| Color | White, Light gray, Tan, Pale yellow | Look at a clean, dry surface in daylight. Color zoning, banding or spots are as diagnostic as the hue. |
|---|---|---|
| Luster | Dull to glassy | Compare a fresh surface with glass and metal; this luster is softer than either. |
| Transparency | Opaque, translucent in thin shards | Hold a thin edge up to a bright light and note whether light passes through. |
| Mohs hardness | 5–6 | It is about as hard as window glass: a knife barely marks it, while a steel file (Mohs 6.5) will. |
| Fracture | Conchoidal, vesicular | Broken surfaces show smooth, curved, shell-like scoops. |
| Specific gravity | 0.25–0.9 | Noticeably light in the hand for its size (specific gravity about 0.575). |
| Crystal system | Amorphous |
Pumice look-alikes and how to tell them apart
Quartz is harder (Mohs 7) than Pumice (Mohs 5–6), so Quartz will scratch Pumice and not the other way round. It is about as hard as window glass: a knife barely marks it, while a steel file (Mohs 6.5) will. Pumice vs Quartz →
Both sit near Mohs 5–6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Pumice vs Rhyolite →
Granite is harder (Mohs 6.5) than Pumice (Mohs 5–6), so Granite will scratch Pumice and not the other way round. It is about as hard as window glass: a knife barely marks it, while a steel file (Mohs 6.5) will. Pumice vs Granite →
Both sit near Mohs 5–6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
Pumice identification FAQ
How can you tell if a rock is Pumice?
Check the color (white, light gray, tan, and pale yellow), the dull to glassy luster, a Mohs hardness of 5–6. Photographing it with the StoneSnap app gives a match in seconds.
What is the hardness of Pumice?
Pumice has a Mohs hardness of 5–6. 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 Pumice and Quartz?
Pumice (Mohs 5–6, dull to glassy luster) and Quartz (Mohs 7, vitreous, greasy on fracture surfaces luster) look alike, but hardness, streak and heft usually separate them. See the full Pumice vs Quartz comparison for a side-by-side table.
Is Pumice worth anything?
Entry-level Pumice specimens sell for around $1, typical collector pieces about $10, and premium examples $75 or more depending on size, quality and locality.
What color is Pumice?
Pumice is most often white, light gray, tan, and pale yellow. Color varies with impurities and locality, so confirm with hardness and luster rather than color alone.
