Marble Identification Guide
How to identify marble, a recrystallized carbonate metamorphic rock, using hardness, the acid fizz test, and its sugary interlocking texture.
Read the full Marble encyclopedia entry →
What Marble Looks Like
Marble is a metamorphic rock formed by recrystallization of limestone or dolostone, composed mainly of interlocking calcite (or dolomite) grains. Pure marble is white, but impurities produce gray, pink, green, yellow, black, and dramatic swirling veins. It has a characteristic sugary, granular texture and a soft, slightly waxy-to-glassy luster.
- Color: white, gray, pink, green, black, veined and mottled
- Luster: dull to glassy; often slightly translucent at edges
- Transparency: translucent in thin pieces, otherwise opaque
- Texture: interlocking granular (saccharoidal/sugary) crystals
Step-by-Step Field ID Checklist
- Test hardness first - marble is soft and can be scratched with a steel knife or even a copper coin (calcite Mohs 3).
- Do the acid test - a drop of dilute hydrochloric acid fizzes vigorously on calcite marble (dolomite marble fizzes only on a scratched/powdered surface).
- Look at the texture - interlocking sugary grains, sometimes glittering with cleavage flashes.
- Check the streak - white.
- Look for veins and swirls rather than fossils or layered bedding.
Key Diagnostic Tests
- Mohs hardness: 3 (calcite) to 3.5-4 (dolomite); scratched by a knife.
- Streak: white.
- Cleavage: the calcite grains show rhombohedral cleavage, visible as tiny reflective flat faces.
- Acid: strong effervescence in dilute HCl - the single most useful field test.
- Specific gravity: about 2.7.
Common Look-Alikes and How to Tell Them Apart
- Limestone: also fizzes in acid, but limestone is a sedimentary rock with a duller, finer or fossil-bearing texture and bedding; marble shows recrystallized interlocking grains and no fossils.
- Quartzite: much harder (Mohs 7), does not fizz in acid, and scratches glass; marble is soft and reactive.
- Onyx marble (cave onyx): a banded calcite formation; also fizzes, but shows fine parallel translucent banding.
- Granite: hard, made of quartz and feldspar crystals, no acid reaction.
Where It Is Typically Found
Marble forms in regional and contact metamorphic belts worldwide. Famous sources include Carrara (Italy), the Greek islands (Paros, Pentelicon), Vermont and Georgia (USA), and many mountain belts where limestone has been metamorphosed.
Frequently asked questions
How can you tell if it's real marble?
Real marble is soft (Mohs 3, scratched by a knife), fizzes when a drop of dilute acid is applied, has a white streak, and shows an interlocking sugary crystalline texture rather than fossils or bedding layers.
What is the difference between marble and limestone?
Both are calcium carbonate and both fizz in acid, but limestone is sedimentary with a fine or fossil-rich texture and visible bedding, while marble is metamorphosed limestone with recrystallized interlocking grains and no fossils.
How do you tell marble from quartzite?
Marble is soft and fizzes in acid; quartzite is hard (Mohs 7), scratches glass, and does not react to acid. The acid test is the quickest separator.
Does marble scratch easily?
Yes. Because it is mostly calcite at Mohs hardness 3, marble can be scratched by a steel knife or even harder coins, which is why it etches and wears under acids and abrasion.
Marble identified by the community
Recent Marble specimens identified with Rock Identifier.
