Identification guide · Metamorphic Rocks
How to Identify Gneiss
Gneiss shows coarse, alternating bands of light minerals, quartz and feldspar, and dark minerals, biotite, hornblende, or garnet, giving it a striped or streaky appearance distinct from the finer, sheet-like foliation of schist. Luster and hardness vary by which mineral band is examined, typically 5.5 to 7 overall due to abundant quartz and feldspar. Streak is generally white since testing usually contacts the felsic bands. It is most often confused with schist and migmatite, but gneiss's coarser, less continuous banding and blockier fracture separate it from schist's more sheet-like fissility.
Gneiss identification checklist
| Color | Gray, Pink, Banded black and white, White | Look at a clean, dry surface in daylight. Color zoning, banding or spots are as diagnostic as the hue. |
|---|---|---|
| Luster | Vitreous to glimmering (mica-rich bands) | Fresh surfaces shine like glass; a dull surface usually means weathering, so chip or wet a corner. |
| Transparency | Opaque | Hold a thin edge up to a bright light and note whether light passes through. |
| Mohs hardness | 6–7 | It scratches glass and a steel knife and cannot be scratched by a steel file. |
| Fracture | Uneven, with foliated parting | |
| Specific gravity | 2.65–2.75 | Ordinary rock-like heft (specific gravity about 2.7), similar to quartz. |
Gneiss look-alikes and how to tell them apart
Both sit near Mohs 6–7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Gneiss vs Migmatite →
Both sit near Mohs 6–7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Gneiss vs Quartz →
Both sit near Mohs 6–7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Gneiss vs Quartzite →
Both sit near Mohs 6–7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
Gneiss identification FAQ
How can you tell if a rock is Gneiss?
Check the color (gray, pink, banded black and white, and white), the vitreous to glimmering (mica-rich bands) luster, a Mohs hardness of 6–7. Photographing it with the StoneSnap app gives a match in seconds.
What is the hardness of Gneiss?
Gneiss has a Mohs hardness of 6–7. It scratches glass and a steel knife and cannot be scratched by a steel file.
What is the difference between Gneiss and Migmatite?
Gneiss (Mohs 6–7, vitreous to glimmering (mica-rich bands) luster) and Migmatite (Mohs 5–7, vitreous to dull (banded) luster) look alike, but hardness, streak and heft usually separate them. See the full Gneiss vs Migmatite comparison for a side-by-side table.
Is Gneiss worth anything?
Entry-level Gneiss 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 Gneiss?
Gneiss is most often gray, pink, banded black and white, and white. Color varies with impurities and locality, so confirm with hardness and luster rather than color alone.
