Tectonic breccias form by intense crushing of bedrock in or near fault zones. They may or may not have additional features, such as veining, serpentinization, chloritization, etc. These rocks consist of large angular pieces surrounded by a fine-grained matrix or finely-crystalline cement.
Tectonic breccia (“French Grand Antique Marble”) (field of view 10.9 cm across) - this attractive tectonic limestone breccia from France consists of black micritic limestone clasts in a whitish carbonate cement. It has been quarried for millennia (known Roman names for this rock include “Marmor Celticum” and “Marmor Aquitanicum”). The rock was exploited in Roman & Byzantine times, then abandoned and forgotten. Quarrying resumed after rediscovery in the 1700s, but the area is now exhausted (it’s an “extinct” quarry rock).
Locality: old quarry at Aubert, just southeast of Moulis, Lez River Valley, southwest of Saint-Girons, western Ariège Department, central Pyrenees Mountains, far-southern France.
Tectonic breccia (“Italian Red Antique Marble”) - this tectonic marble breccia consists of reddish marble clasts with some white calcite veining and minor serpentinization (greenish areas).
Locality: Genoa, Liguria Province, Apenine Mountains, northwestern Italy.