This is a cluster of marcasite crystals that's associated with rhombohedral barite crystals and a small aggregation of quartz, collected from the Bou Nahas Mine (Bou N'hass Mine) in the Oumjrane area of Morocco.
Barite, commonly spelled baryte, is well-known for its great range of colors and varied crystal forms and habits. It is a heavy mineral consisting of barium sulfate, and typically has the chemical formula of BaSO4. The barite group consists of baryte, celestine, anglesite and anhydrite. It's generally white to colorless and is the main source of barium.