The quarry of Quenast is a porphyry deposit, set on a 350ha area.
The site is located by the village of Quenast, on the south-west side of Brussels.
In the past, the quarry produced road pavements that were exported well beyond the Belgian borders. The site is equipped with a rail road connection and is located near the Tournai-Brussels highway.
The Quenast quarry is a site of high biological interest, which includes a nice population of Naterjack Toads.
In the area, nearby the small town of Lessines, other ancient Porphyry quarries are also known for their biological interest, especially the silicious fallow lands, sheltering rare plants such as Filago minima, other dwarf annual species, and numerous Orchids like Dactylorhiza fuschii, Dactylorhiza praetermissa or Ophrys apifera.