Potomac Marble is a decorative sedimentary rock composed of rounded limestone clasts cemented together in a colorful matrix. It is famous in American history for being used in the columns of the U.S. Capitol building and is often found as a polished stone in architectural or display collections.
Is this potomac marble?
3-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch potomac marble with a known reference. Potomac Marble sits at Mohs 3-4, softer than the next harder reference, harder than the previous one.
- 2Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 3Match the color rangeCompare against the expected color range: red, green, brown, white.
Often confused with
Potomac Marble vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside potomac marble
Minerals reported to co-occur with potomac marble. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Mohs hardness
- 3-4
- Density
- 2.6-2.8 g/cm³
- Luster
- Vitreous
- Transparency
- Opaque
- Rarity
- Common
- Uses
- Ornamental, Decorative, Lapidary
- Host rock
- sedimentary
Where rockhounds find potomac marble
1 mapped spotsClassic worldwide localities
- Maryland, USA
- Potomac River Valley, USA
Field-hunting tip
Where it forms: sedimentary. If you start seeing calcite, dolomite in float, you are in the right ground. In the U.S., the densest reported localities are in Pennsylvania. Start trip planning there.
More potomac marble photos
Common questions
How do you identify potomac marble?+
Where is potomac marble found?+
Can I find potomac marble in the United States?+
What rocks look like potomac marble?+
What minerals are found with potomac marble?+
What kind of rock does potomac marble form in?+
What is potomac marble used for?+
Find potomac marble on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
