The four exposed rock formations are the basaltic tops of a submarine volcanic cone, heavily eroded by the sea and frequently immersed completely by waves during inclement weather.

[1] However, the Fradinhos are part of larger rock formations which slope up to sea level rather steeply from the surrounding ocean floor.

The underwater environment in the area is characterized by lava flows with various caverns, slopes, and fractures—all eroded by the sea over time—which is typical in the volcanically-formed Azores.

Its waters are home to Azores chromis (Chromis limbata), barred hogfish, black corals, groupers, Mediterranean parrotfish (Sparisoma cretense), red scorpionfish (Scorpaena scrofa), oysters, slipper lobsters (family Scyllaridae), and European spider crab (Maja squinado).

However, due to their location in open ocean relatively far off the coast, strong currents, and caverns up to 30 metres (98 ft) deep, only experienced divers should attempt a visit.