two polished septarian spheres


The name septarian comes from the Latin word septum meaning a dividing partition between two tissues or cavities and today the word septum is used to describe the fleshy partition between the nostrils. Septarian which s a rock not a mineral is a kind of mud ball that dates back millions of years.  Its unique appearance and the fact that it takes on an exceptionally high polish has led to it becoming popular as a lapidary material.  This eye-catching rock is unlike any other and when used as a gemstone it tends to be cut as a cabochon.

Describing exactly how septarian formed is no easy task and there are many different views and interpretations about how the stone evolved.  Numerous questions remain unanswered and it's a topic that continues to puzzle geologists however the general process is considered to be relatively common in sedimentary rocks. What's known for certain is that septarian formed during the Cretaceous Period which began approximately 145 million years ago and ended 66 million years ago which is about the time the dinosaurs disappeared.

Although often referred to as septarian this rock is more accurately known as a septarian nodule or concretion.  Both structures are closely related and the terms are often used interchangeably. To keep things simple, in geology a nodule refers to a small irregularly shaped knot, mass or lump of crystals or particles with a contrasting composition which means they're not all the same and may even be separated from the formation in which they occurred. A concretion on the other hand is a body of rock enclosed within sediments that are generally softer and of the same composition as the formation in which they occurred. The word concretion comes from the Latin meaning 'to grow together' or 'harden' and these structures are often looked upon as being geological curiosities because of the many unusual shapes, sizes and compositions in which they can occur.


septarian nodule in a museum display cabinet 

Septarian nodule. Natural History Museum London | Photo: Stone Mania ©


Basically septarian nodules or concretions formed in water when a quantity of minerals and organic matter surrounded a centre mass and gradually over millions of years and with the help of various natural processes, hardened and became cemented together. The minerals may include sandstone which is compacted grains of sand, shale which is compacted mud, siltstone (fine grained silt, sand, clay or other material carried by water and subsequently deposited as a sediment) or limestone which is made up primarily of calcium carbonate.  Whilst the exterior of septarian nodules feature a network of ridges that can give them the appearance of turtle shells, the interiors contain distinctive angular cavities or cracks known as 'septaria' which comes from the Latin word septum. It's not known for certain exactly how the cracks and cavities formed but the most popular theories suggest they were either caused by dehydration or shrinkage of clay or organic matter in the centre of the structure, expansion of gases which may have been caused by decaying organic matter or fracturing or shrinkage caused by earthquakes or compaction.

Septarian concretions are thought to have been formed in shallow lakes as the tide caused the accumulated mass to roll back and forth and in doing so it built up layers of sticky mud which would then have dried out during the hotter months when the water receded. The mud balls were then buried under sediment and the cracks as and when they occurred, were filled through seepage with a crystalline substance such as silica or calcite from shells of dead marine creatures. Crystals subsequently formed which can be seen as the bright yellow centres of septarian.  A thin wall of calcite was also transformed into transformed into aragonite or siderite which separated the heavy clay exteriors from the crystallized centre.

Septarian is composed of the mineral calcite (yellow centre), aragonite or siderite (the brown lines) and limestone which is the outer rock.

In the world of crystal healing and also according to Judy Hall's Crystal Bible, septarian is said encourage one to take care of the earth.  It harmonizes emotions and is overall a happy stone which helps with new ideas and the enthusiasm to then follow them through. It enhances the ability to communicate within a group and is emotionally nourishing and calming.



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