The septaria is a geological formation composed mainly of calcite and clay, characterized by the presence of fissures which separate the different parts of the rock. The formation of the septaria takes place through a process of sedimentation and dioxidation.
Here is a general description of the formation process of the septaries:

Sedimentation: Initially, dead marine organisms and other sediment particles settle to the bottom of a body of water such as an ocean or lake. Over millions of years, layers of sediment build up on top of each other.

Compressed: The continuous overlapping of sediments causes high pressure on the lower parts, which tend to become more and more compact.

Mineral Seepage: During the sedimentation process, the water surrounding the sediments contains dissolved minerals such as calcite. These minerals can infiltrate cracks or cavities in the rock, gradually settling over time.

Dioxidative Process: Over time, water containing dissolved minerals seeps into cracks in the sediments. During this process, the chemical reactions between the water and the minerals cause dioxidation, i.e. the oxidation of the organic substances present in the rock.

Fissure Formation: During dioxidation, an expansion and contraction process occurs within the rock. This process creates tensions which lead to the formation of cracks or fissures in the rock. The fissures can extend and branch over time, creating a lattice structure typical of septaria.

Deposition of Secondary Minerals: The fissures formed in the septaria provide an ideal environment for the deposition of secondary minerals. During the passage of water through these fissures, minerals such as calcite, aragonite or hematite may precipitate. These minerals fill in the fissures and create the distinctive patterns and colorations of the septaria.