period: Upper Carboniferous (358.9-298.9 million years ago)

excavation site: Flora mine pit, Dąbrowa Górnicza (Upper Silesia)

Concretion is a compact mineral mass created as a result of gradual precipitation of minerals around an object in a rock – it can be a roundstone, fossil or even a grain of sand. The core of the concretion remains unknown. The precipitation always occurs from the core outwards, forming the concretion in a spherical shape. The inner composition of the concretion is often concentric or concentric-radial.

The piece comes from the collection of Geological Museum of the National Geological Institute – National Research Institute.