A large majority of the septarian concretions come from Utah. However, while looking for ammonites, we stumbled across an area of septarian concretions within the Eagle Ford Formation in Texas.
Septarian concretions formed on the Cretaceous seafloor about 50-70 million years ago. There are several theories as to how septarian concretions were formed. The primary theory is they were mud balls. These mud balls formed around a nucleus, which is something in the center, like a shell or ammonite. As the mud ball rolled around on the ocean floor, it picked up more remains of shelled sea life.
As the oceans receded, the mud balls cracked. Minerals from the water, sea life shells, and surrounding mud layers seeped into the cracks over time. The cracks were filled with crystals of calcite and aragonite to form walls or septa. These septa can give the concretions their unusual texture on the outside. Still, at times, they have smooth exteriors with calcite or aragonite veins on the interior.
Their exterior textures and interior colors vary greatly. Their sizes also range widely from only a few inches to over 6 feet across.
The septarian concretions were called “dragon stone” because the exterior patterns or unusual texture on the stones resembled dragon scales. According to the Malagasy legend, when the “dragons” died out, they fossilized and became part of the seabed and the stone. People often misidentify a septarian concretion as a fossilized egg or turtle shell.
When cut, the inside of a septarian concretion is just as beautiful and unique. The septarian concretions contain clay/limestone that is blue-gray, rust-red, tan, or brown. The lines forming the septa within the concretions are brown aragonite, yellow to white calcite, and sometimes white barite. Usually, the aragonite gets deposited first, and then calcite crystals grow on top of these deposits.
At times, pyrite may be found in clumps, or dispersed throughout the gray clay/limestone. When prepared, the slabs or geodes containing dispersed pyrite produce a metallic gleam. They also smell like sulfur or rotten eggs when cut. The concretions can be prepared as slabs, or if they contain a hollow (called a vug) kept as a geode. Our septarian creations range in size from 2 inches to 14 inches. Some of the septarians are shaped into either freeform designs or specific shapes. To view septarian concretions for sale, visit: https://fossilfanatics.com/product-category/texas-septarian-concretions/
Shelled sea life remains may also be found within the septarian concretions. Below is an ammonite that was extracted from a septarian concretion. It has a calcite and aragonite vein running through it.
These Texas septarians were found, prepared and proudly brought to you by Fossil Fanatics LLC.