Concretion
Concretion is sedimentary (diagenetic nodule), (calcite/siderite/silica-cemented sediment). In the hand, it rates 3 to 6 (cement-dependent) on the Mohs scale, and it runs gray and tan. Suspiciously smooth rounded stone 'sculptures', balls, discs, and fused blobs, grown by minerals cementing sediment around a nucleus, often with a fossil at the center.
The geology.
Concretion carries the formula (calcite/siderite/silica-cemented sediment). It belongs to the, system. Catalogues list it as sedimentary (diagenetic nodule).
It sits at 3 to 6 (cement-dependent) on the Mohs scale. The surface reads dull, earthy. Light behaviour is opaque. Specific gravity runs 2.2 to 3.0. The streak is,. It breaks with uneven; often concentrically layered.
Suspiciously smooth rounded stone 'sculptures', balls, discs, and fused blobs, grown by minerals cementing sediment around a nucleus, often with a fossil at the center.
It reaches buyers as round balls, discs, dumbbells or sculptural 'fairy stone' clusters.
The origins.
Shales and sandstones worldwide; famous fields: Moeraki boulders (New Zealand), Kansas 'cannonballs', Quebec fairy stones.
On value, the database notes: common and affordable; sculptural forms charm collectors.
Traditional associations.
In energy work traditions, concretions like fairy stones carry folk associations of protection and good luck.
We keep this section because people ask. It sits below the geology on purpose, and none of it describes something the stone does.
Spotting the real thing.
Suspiciously smooth rounded stone 'sculptures', balls, discs, and fused blobs, grown by minerals cementing sediment around a nucleus, often with a fossil at the center.
Sold online as 'dinosaur eggs' depressingly often, shell pores and bone texture are absent in concretions.
| Looks like | How to tell them apart |
|---|---|
| Dinosaur eggs (hopeful) | Real eggs show shell texture with pores; concretions are uniform cemented sediment, nearly all 'egg' finds are concretions |
| Moqui marbles | Moquis are the iron-shelled sandstone special case, see their own entry |
| Cannonballs | Iron rusts and rings metallic; concretions are stone |
At-home tests.
Before anyone talks you into a lab report, these are the checks worth doing yourself on concretion.
| Test | What you should see |
|---|---|
| By eye | Concentric internal layering when broken |
| Acid check | Calcite-cemented types fizz |
| By eye | Often a fossil or shell at the core |
Destructive tests belong to a gemologist, not a kitchen table. If a piece matters to you, pay for an appraisal before you take a file to it.
Care & handling.
At 3 to 6 (cement-dependent) on the Mohs scale this is a soft material. Keep it as a display piece, store it apart from harder stones, and skip daily-wear settings.
It breaks with uneven; often concentrically layered, which is worth knowing before you set it or drop it.
Clean it by hand, dry it properly, and keep it away from ultrasonic cleaners and hot steam.
A deeper look.
Extended detail on composition, sourcing, authentication and market value.
The physical record
The formula on record is (calcite/siderite/silica-cemented sediment). Crystal system:,. Specific gravity: 2.2 to 3.0. Streak:,. Cleavage and fracture: Uneven; often concentrically layered.
How it reaches the market
Shales and sandstones worldwide; famous fields: Moeraki boulders (New Zealand), Kansas 'cannonballs', Quebec fairy stones.
What it gets confused with
Dinosaur eggs (hopeful): Real eggs show shell texture with pores; concretions are uniform cemented sediment, nearly all 'egg' finds are concretions. Moqui marbles: Moquis are the iron-shelled sandstone special case, see their own entry. Cannonballs: Iron rusts and rings metallic; concretions are stone.
What it is worth
Common and affordable; sculptural forms charm collectors.
Where buyers get caught
Sold online as 'dinosaur eggs' depressingly often, shell pores and bone texture are absent in concretions.
One more thing
New Zealand's two-meter Moeraki boulders are concretions that took four million years each to grow on the seafloor.
An education-first guide.
We do not stock concretion. Writing it up regardless is the point of a reference library.
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