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Septarian Nodule or Concretion | Properties Facts and Photos



round septarian nodule filled with yellow calcite crystals. On a black background



1. Septarian from the Latin 'Septum'
2. Septarian Nodule Geological Curiosity
3. Formation of Septarian
4. Septarian Concretions Moeraki Boulders
5. Septarian Healing Properties
6. Article Photos
7. Septarian | Explore Our Collection
8. Read More



Septarian from the Latin Word Septum

A septarian nodule is a type of rock whose name comes from the Latin word septum meaning a dividing partition between two tissues or cavities.  In anatomy the word septum is used to describe the cartilage in our nose that separates one nostril from the other.  Septarian nodules are exceptionally distinctive, take on a high polish and are classified as a rock not a mineral.  Rocks are made up of minerals wheras minerals are made up of crystals.

Septarian nodules are made up primarily of three different minerals.  The yellow centre is calcite, the brown coloured lines are aragonite or siderite and the outer rock is limestone.  Septarian nodules are sometimes likened to prehistoric mud balls because of the way they formed.



Septarian Nodule Geological Curiosity

Although often known simply as septarian it's more accurate to refer to these structures as nodules or concretions.  Both are quite similar hence the terms tend to be used interchangeably.  In geology a nodule refers to a small irregularly shaped mass or lump of crystals or particles with a contrasting composition.  That basically means they're not all the same and may even be separated from the formation in which they occurred. A concretion is a self contained cemented body of sediment.  The word also comes from Latin and means 'to grow together' or 'to harden'.

Despite being quite common concretions are considered to be geological curiosities because of the many unusual shapes, sizes and compositions in which they occur.


septarian nodule in the Natural History Museum London




Formation of a Septarian Nodule

Septarian is known to have formed during the Cretaceous Period which began approximately one hundred and forty five million years ago and ended sixty six million years ago around the time the dinosaurs disappeared.  They formed in bodies of water as minerals and organic matter accumulated around a centre mass and gradually over millions of years and with the help of various geological processes, hardened and became cemented together forming a nodule.

The minerals are likely to have included sandstone which is compacted grains of sand, shale which is compacted mud, siltstone and limestone which is primarily calcium carbonate.  The mineral aragonite is the crystal form of calcium carbonate which is a chemical compound that occurs naturally in rocks most notably as limestone.  Siltstone is fine grained silt, sand, clay or other materials that are carried in water before being deposited as sediment. 

Septarian nodules may well have formed in shallow lakes as the tide caused an accumulated mass to gently roll back and forth.  As the process continued the mass built up layers of sticky mud which subsequently dried out during the hotter months as the water receded. The mud balls were then buried under sediment and any cracks that appeared slowly filled by means of seepage with a coarse crystalline substance such as silica (quartz) or calcite (from the shells of dead marine creatures). The crystals which later formed are the bright yellow centres of the septarian nodule.  A thin wall of calcite was also transformed into aragonite or siderite which separated the heavy clay exterior from the crystallized centre.



three polished septarian nodule spheres



Whilst the exterior of the septarian nodule was hard and featured a network of ridges, the interior contained distinctive angular cavities or cracks known as 'septaria' from the Latin word septum.  It's believed these were caused by the dehydration and shrinkage of clay although some suggest they may have been caused by the expansion of gases generated by decaying organic matter in the centre of the nodule.  They may also have been caused by fracturing or shrinkage caused by earthquakes or compaction.

Irrespective of how the cracks formed, they subsequently filled with hardened natural minerals as groundwater changed and receded.  The minerals in the vast majority of cases were silica or calcite. 

Describing precisely how septarian nodules formed is not easy and there are many different views and interpretations.  Numerous questions remain unanswered and it's an ongoing topic of debate amongst geologists however the general formation process is one that's relatively common in sedimentary rocks.




Large Septarian Concretions | Moeraki Boulders 

The moeraki boulders are large grey coloured septarian concretions that can be found on a stretch of coastline in New Zealand.  The boulders which were buried for millions of years beneath mudstone began to appear because of erosion from coastal cliffs.  In years to come more will emerge from the mudstone as geological changes continue to reshape the landscape.  It's believed the largest concretions took about four million years to get to their current size.

Spherical boulders that are almost identical can also be found close to Hokianga Harbour on the North Island and similar concretions can be found in many countries around the world.  The Moeraki boulders are famous primarily because of their spherical shape and size.



Large spherical stone structures on the beach. Known as the Moeraki Boulders

Clickable image



Septarian Nodule Healing Properties

The healing properties of a septarian nodule include encouraging us to take care of the earth.  On a spiritual level it harmonises emotions with intellect, creates new ideas and the enthusiasm to follow them through.  It breaks repetitive routines or patterns of behaviour, extends patience and increases tolerance and endurance.  A joyful stone that's emotionally nourishing and calming, it can offer support for those who speak in public and can help improve communication within a small group.

Septarian is often used by healers because it's a tool for nurturing and showing care for others.  It has powerful healing abilities and is recommended for SAD (seasonal affective disorder). 



Article Photos

The photo of the septarian nodule at the top of our page is courtesy of Stan Celestian (Flickr). The stone in the second photo is on display in London's Natural History Museum, the spheres are from our own collection.  Both photos were taken by Stone Mania ©.  The photos are clickable and redirect to the original full size image.  Clicking the third photo redirects to an amazing photograph of the Moeraki Boulders on Koekohe Beach on the east coast of New Zealand's South Island.



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