This is a so-called "black" calcite from the Gralex quarry, Mont-sur-Marchienne (near Charleroi), Hainout Province, Belgium.
These crystals are darker than usual and appear etched or perhaps fractured and cured afterwards. Anyhow, the grooves in the crystals have been filled with a strongly fluorescent material. I have no clue what it is but is follows the crystal structure of calcite. The photos are taken in halogen light and in defocussed violet laser light of 405 nm.
