Identification guide · Igneous Rocks
How to Identify Scoria
Scoria is dark reddish-brown to black, riddled with rounded to irregular gas-bubble cavities called vesicles, giving it a rough, popcorn-like texture. It feels notably lighter than a solid rock of the same size but is dense enough to sink in water, unlike pumice, which floats. Hardness reflects its basaltic mineral content, roughly 5 to 6, though the vesicular structure makes it crumble more easily than solid rock. It is most often confused with pumice, which is lighter-colored, more silica-rich, and buoyant.
Scoria identification checklist
| Color | Dark red, Black, Brown, Reddish brown | Look at a clean, dry surface in daylight. Color zoning, banding or spots are as diagnostic as the hue. |
|---|---|---|
| Luster | Dull, glassy | Compare a fresh surface with glass and metal; this luster is softer than either. |
| Transparency | Opaque | 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 | Irregular, vesicular | |
| Specific gravity | 1.5–2.6 | Noticeably light in the hand for its size (specific gravity about 2.05). |
Scoria look-alikes and how to tell them apart
Quartz is harder (Mohs 7) than Scoria (Mohs 5–6), so Quartz will scratch Scoria 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. Scoria vs Quartz →
Both sit near Mohs 5–6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Scoria vs Andesite →
Both sit near Mohs 5–6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Scoria vs Rhyolite →
Both sit near Mohs 5–6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
Scoria identification FAQ
How can you tell if a rock is Scoria?
Check the color (dark red, black, brown, and reddish brown), the dull, glassy luster, a Mohs hardness of 5–6. Photographing it with the StoneSnap app gives a match in seconds.
What is the hardness of Scoria?
Scoria 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 Scoria and Quartz?
Scoria (Mohs 5–6, dull, 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 Scoria vs Quartz comparison for a side-by-side table.
Is Scoria worth anything?
Entry-level Scoria 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 Scoria?
Scoria is most often dark red, black, brown, and reddish brown. Color varies with impurities and locality, so confirm with hardness and luster rather than color alone.
