The name septarian comes from the Latin word septum meaning a dividing partition between two tissues or cavities and today septum is used to describe the fleshy partition between the nostrils. Septarian is a kind of mud ball that dates back millions of years and its unique appearance and the fact that it takes on a high polish has led to it becoming popular as a lapidary material. It's an eye-catching stone which is unlike any other, when used in jewellery it's cut as a cabochon.
Describing exactly how septarian was formed is no easy task and there are many different views and interpretations about how these structures evolved. Many questions remain unanswered surrounding certain aspects of their formation and it's a topic which continues to puzzle geologists. The overall process however is considered to be relatively common in all sedimentary rocks. One thing that's known for sure is that septarian was 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 vanished from the face of the earth.
Although often referred to simply as septarian, this distinctive 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 it's different and may even be separated from the formation in which it 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 it occurred. Concretion comes from the Latin word 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.
Inside of a concretion and septarian nodule. Natural History Museum | 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 which is fine grained silt (sand, clay or other material carried by water and subsequently deposited as a sediment) or limestone which is made up of calcium carbonate. Whilst the exterior of septarian nodules feature a network of ridges which can give them the appearance of turtle shells, the interiors contain distinctive angular cavities or cracks which are known as "septaria" from the Latin word septum. It's not known for certain exactly how these cracks and cavities formed but the most popular theories indicate 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 as a result of 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 the shells of dead marine creatures. Crystals subsequently formed and these can be seen as the bright yellow centres of septarian. A thin wall of calcite was also transformed into aragonite or siderite which separated the heavy clay exteriors from the crystallized centre.
Septarian is composed of calcite (the yellow centre), aragonite or siderite (the brown lines) and limestone which is the outer rock.
In the world of crystal healing and according to Judy Hall's Crystal Bible, septarian is said encourage one to take care of the earth, it harmonizes the 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.