XM2130NTB: Dark brown semicircular nodule formed by a marly rock matrix in which there is a radiating polygonal network filled with Calcite crystals with colors that vary from white to brown, some of them very dark brown. These formations are known as septaria (or septarian concretions). They have shrinkage cracks that originated from loss of water in a mass of clay group mineral gels with subsequent recrystallization. Comes from a well-known locality in the flysch facies of Deva, in Guipúzcoa, Spain. Today it is forbidden to collect this type of specimen as the locality has been declared an LIG (Site of Geological Interest) and only pieces from old collections, like this one, are available.
Deva, Municipio Deva, Comarca Bajo Deva, Guipúzcoa / Gipuzkoa, Basque Country (Euskadi)  Spain

Specimen size: 7.8 × 7.7 × 2.7 cm = 3.07” × 3.03” × 1.06”