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, 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.