Photos

This is a single cristal on matrix. The mineral is called pyrite, from the Greek word Pyrrhos, which means fire. First uses of pyrite were for making fire.
That cristal is natural, not cut, not polished, only extracted from its matrix for the pleasure of our eyes.
Cristalline system of pyrite is of course cubic, this is one of the perfect illustrations of that system.
Chemically, this is an iron sulphur (FeS2) which is quite stable, not the same as marcassite (FeS2 too) which alters fast if not treated.
That piece is from Navajùn, a big quarry in La Rioja, Spain. The cristal is about 3,5 centimeters (1,6 - 1,7 inch).
My choice to set that picture in architecture is directed by the fact that every human construction is inspired by Nature's art, especially minerals.
Artificial light.
Additional light (yellow) to enhance the "fire" aspect
Background changed into black (Photoshop).