A nodule is a rounded, irregular mass or concretion formed by mineral precipitation around a central nucleus within sedimentary rock. Collectors prize it for what may be inside: a quartz or chalcedony-lined geode, fossilized material, or an unusual crystalline structure. It commonly weathers out of softer host rock such as chalk beds or shale.

sedimentarycommon

Nodule

Is this nodule?

3-step field check

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

1
Read the texture
Look at a fresh break with a hand lens. Texture: Small, irregularly rounded lump that contrasts with the enclosing sediment or rock.
2
Pick out the minerals
Composition: Commonly calcite, chert, apatite (phosphorite), anhydrite or pyrite. Identify the two or three most abundant grains.
3
Match the color range
Compare against the expected color range: gray, brown, black, white.

Often found alongside nodule

Minerals reported to co-occur with nodule. Spotting these in float or country rock is a strong cue you are in the right ground.

All properties

Colors: Gray Brown Black White
Rarity: Common
Uses: Collector, Lapidary
Host rock: sedimentary strata such as limestone, chalk, or shale
Texture: Small, irregularly rounded lump that contrasts with the enclosing sediment or rock
Composition: Commonly calcite, chert, apatite (phosphorite), anhydrite or pyrite

Where rockhounds find nodule

10 mapped spots

Classic worldwide localities

United Kingdom
United States
France
Germany
Poland

Field-hunting tip

Where it forms: sedimentary strata such as limestone, chalk, or shale. If you start seeing chalcedony, calcite, pyrite in float, you are in the right ground. In the U.S., the densest reported localities are in Arizona, Nevada, Utah. Start trip planning there.

Browse 10 U.S. spots for nodule →

More nodule photos

Common questions

Where is nodule found?+

Notable localities include United Kingdom; United States; France; Germany; Poland.

Can I find nodule in the United States?+

RockHoundR maps 10 nodule rockhounding spots across 6 U.S. states. The top states are Arizona, Nevada, Utah.

What minerals are found with nodule?+

Nodule commonly co-occurs with chalcedony, calcite, pyrite, dolomite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does nodule form in?+

Where it forms: sedimentary strata such as limestone, chalk, or shale. Working float back to the host body is the standard way to chase a fresh occurrence.

What is nodule used for?+

Nodule is used in collector, lapidary.

Find nodule on the map

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