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✅ SOLVED Need help Identifing a weird rock.
- Thread starter BobMaz
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Red-Coat
Gold Member
Welcome to Tnet.
The concentric banding tells you this has formed by a concretionary process. Although it has a nodular form, the geological distinction is that a concretion is formed around a nucleus by progressive precipitation of minerals (hence the concentric banding), whereas a nodule is a replacement body. Most variants of quartz lend themselves to this process, notably cherts, and I think that's most likely what you have.
The process is often triggered by chemical decomposition of something organic acting as a nucleus which may determine the ultimate shape to some extent, but all kinds of shapes are possible and - inevitably - rounded or egg-like shapes are common.
Soft fruits with a high water content such as lemons don't fossilise to produce three-dimensional representations of their original form like that. The shape is just coincidental.
The concentric banding tells you this has formed by a concretionary process. Although it has a nodular form, the geological distinction is that a concretion is formed around a nucleus by progressive precipitation of minerals (hence the concentric banding), whereas a nodule is a replacement body. Most variants of quartz lend themselves to this process, notably cherts, and I think that's most likely what you have.
The process is often triggered by chemical decomposition of something organic acting as a nucleus which may determine the ultimate shape to some extent, but all kinds of shapes are possible and - inevitably - rounded or egg-like shapes are common.
Soft fruits with a high water content such as lemons don't fossilise to produce three-dimensional representations of their original form like that. The shape is just coincidental.
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