calcite crystals in cystoid (echinosphaerites aurantium)

calcite crystals ordovician cystoid echinosphaerites aurentium paleozoic cysts sea bubble echinoderm active formation geology geoscience greece mountain rock rocky terrain graphic texture colour color nature pattern background stone colours shades orange eroded effect beautiful beauty natural brown abstract mineral view simplicity greek rugged circular fossil geode lower silurian spherical aurantium cystoidea white echinodermata found mount hymettus