GYPSUM

CLASS: Sulfate . . . CHEMICAL FORMULA: CaSO4 . 2H20 . . . CRYSTAL SYSTEM: monoclinic
CRYSTAL FORM: prism, pinacoid; tabular crystals (usually twinned), fibrous, granular, massive and rosette formations.
COLOR: colorless, white, grey, yellow, reddish .
PHYSICAL PROPERTIES: soft (2 Mohs), light (2,35 g/cm3), fragile, exfoliable in sheets, transparent/translucent/opaque, vitreous/silky luster and pearly on the exfoliation surfaces, soluble in hydrochloric acid and hot water, some varieties are fluorescent to ultraviolet rays.
CURIOSITIES: related to the improvement of clarity of ideas