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.

Hardness

3-4

Mohs

Luster

Vitreous

Streak

White

Transparency

Opaque

sedimentarycommon

Potomac Marble

Also: Calico Stone, Maryland Marble

Hardness: 3-4
Luster: Vitreous
Streak: White
Transparency: Opaque

No image

Is this potomac marble?

5-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

1
Test the hardness
Try 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.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Potomac Marble leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Potomac Marble typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: red, green, brown, white.
5
Look at form & habit
Typical habit: massive.

Often confused with

Potomac Marble vs. its common look-alikes, and how to tell them apart in the field.

sedimentary

Breccia

Mohs 3-7

How to tell apart: Streak differs, so Potomac Marble leaves white, Breccia leaves variable; luster reads vitreous on Potomac Marble and dull on Breccia.

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
Colors: Red Green Brown White
Streak: White
Luster: Vitreous
Transparency: Opaque
Crystal habit: Massive
Cleavage: None
Rarity: Common
Uses: Ornamental, Decorative, Lapidary
Host rock: Sedimentary
Typical price: $10-100 per specimen

Where rockhounds find potomac marble

1 mapped spots

Classic worldwide localities

Maryland, USA
Potomac River Valley, USA

Field-hunting tip

Look in sedimentary country, the host setting where potomac marble typically forms. If you start seeing calcite, dolomite in float, you are in the right ground. Field specimens usually show a massive habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Pennsylvania. Start trip planning there.

Browse 1 U.S. spots for potomac marble →

Common questions

How do you identify potomac marble?+

Mohs hardness is 3-4. It typically shows a vitreous luster. The streak is white. Common colors include red, green, brown, white.

Where is potomac marble found?+

Notable localities include Maryland, USA; Potomac River Valley, USA.

Can I find potomac marble in the United States?+

RockHoundR maps 1 potomac marble rockhounding spots across 1 U.S. states. The top states are Pennsylvania.

How much is potomac marble worth?+

Typical asking prices fall in the range of $10-100 per specimen. Quality, size, and provenance can move individual specimens well outside that range.

What rocks look like potomac marble?+

Potomac Marble is most often confused with Breccia, Puddingstone. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with potomac marble?+

Potomac Marble commonly co-occurs with Calcite, Dolomite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does potomac marble form in?+

Potomac Marble typically forms in sedimentary. Working float back to the host body is the standard way to chase a fresh occurrence.

What is potomac marble used for?+

Potomac Marble is used in ornamental, decorative, lapidary.

Find potomac marble on the map

RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.