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The cerebroids (from Latin cerebrum brain and the Greek eidos aspect) are nodules with silica that occur in the limestone massif of Estremadura usually associated with Chão de Pias limestone (upper Bajocian - Middle Jurassic). Although they have been associated with fossil structures, they have not yet been properly studied so its origin isn’t fully clarified. They have the shape of bunch of grapes or a convoluted one (e. g. winding), resembling a brain, while the internal structure, when viewed in section, is in layers.

Commonly they are found in the walls in some places at Sto. António plateau, in particular near the village of Serra de Sto. António, and are rarely found in its places of origin.

In the Simplified Geological Map of Serras de Aire e Candeeiros Nature Park, cerebroides can be observed in an accumulation of blocks near that location.

Jurassic - geological period in which the dinosaurs dominated and the development of vegetation was abundant. It lasted about 54 million years, roughly between 208 to 144 million years ago.