Gastroliths are stones swallowed by animals, such as dinosaurs or modern birds, to aid in digestion by grinding food in the gizzard. Collectors should look for specimens displaying unique high-polish surfaces created by gastric churning, often found associated with articulated dinosaur skeletons.

Hardness

variable

Mohs

Luster

Variable

Transparency

Opaque

fossiluncommon

Gastroliths

Also: stomach stones, gizzard stones

Hardness: variable
Luster: Variable
Transparency: Opaque

Is this gastroliths?

4-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 gastroliths with a known reference. Gastroliths sits at Mohs variable — softer than the next harder reference, harder than the previous one.
2
Read the luster
Hold the specimen under a strong light. Gastroliths typically shows a variable luster.
3
Match the color range
Compare against the expected color range: variable, brown, gray, black, red, tan.
4
Look at form & habit
Typical habit: rounded, polished surface.

Often found alongside gastroliths

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

Dinosaur Bones
fossil · Mohs 5.5-7

All properties

Mohs hardness: variable
Density: variable
Colors: Variable Brown Gray Black Red Tan
Luster: Variable
Transparency: Opaque
Crystal habit: Rounded, Polished Surface
Cleavage: None
Rarity: Uncommon
Uses: Collector, Scientific Research, Paleontological Study
Host rock: Sedimentary Deposits
Typical price: $10-200 per specimen depending on provenance and size

Where rockhounds find gastroliths

4 mapped spots

Classic worldwide localities

Morrison Formation, USA
Glen Rose Formation, USA
Winton Formation, Australia
Gobi Desert, Mongolia

Field-hunting tip

Look in sedimentary deposits country — that is the host setting where gastroliths typically forms. If you start seeing dinosaur bones, fossilized teeth in float, you are in the right ground. Field specimens usually show a rounded, polished surface habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Wyoming — start trip planning there.

Browse 4 U.S. spots for gastroliths →

Common questions

How do you identify gastroliths?+

Mohs hardness is variable. It typically shows a variable luster. Common colors include variable, brown, gray, black.

Where is gastroliths found?+

Notable localities include Morrison Formation, USA; Glen Rose Formation, USA; Winton Formation, Australia; Gobi Desert, Mongolia.

Can I find gastroliths in the United States?+

RockHoundR maps 4 gastroliths rockhounding spots across 1 U.S. states — the top states are Wyoming.

How much is gastroliths worth?+

Typical asking prices fall in the range of $10-200 per specimen depending on provenance and size. Quality, size, and provenance can move individual specimens well outside that range.

What minerals are found with gastroliths?+

Gastroliths commonly co-occurs with dinosaur bones, fossilized teeth. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does gastroliths form in?+

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

What is gastroliths used for?+

Gastroliths is used in collector, scientific research, paleontological study.

Find gastroliths on the map

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