Saco do Inferninho is a Cenozoic basalt outcrop associated with the Macau Magmatism of the Borborema Province.

It is located in the rural area of Picuí (Barra do Cipó region) and is a popular destination for hiking trails and field trips. Saco do Inferninho is a Cenozoic basalt outcrop in northern Picuí, associated with the Macau Magmatism of the Borborema Province; it is a basalt plug/intrusion (containing olivine and columnar jointing), not an active volcano.

The site is popularly known as the “Picuí volcano” because the volcanic rocks (basalts) lead people to interpret it as such; however, researchers explain that the feature results from the outflow or ascent of basic magma and does not constitute a volcanic cone.