I made my own Fluorescent and Phosphorescent Calcite!

Hard water leaves behind calcite, which is a form of calcium carbonate, when it evaporates because the primary mineral causing hard water is dissolved calcium, which precipitates out as calcite when the water dries, leaving behind a visible deposit on surfaces like dishes, shower walls, and faucets.
They are usually calcium carbonate or magnesium.

[@littlepieceofwork]

Ah! So cool!

[@Muonium1]

Hah! I noticed this too on the limescale around my faucets! I assumed maybe it was dolomite due to the magnesium content. I really wonder what's causing the phosphorescence now, since this is so very similar to scalenohedral / dogtooth calcite and other speleothemic origin calcite. I always read this was caused by the humic and fulvic acids imparted to groundwater by decaying plant matter in soil above the cave where such calcite formed, but obviously there's none of that here! Maybe calcite is just intrinsically phosphorescent! I wonder if you could induce the red fluorescence of eg. Franklin_Ogdensberg calcite here by sprinkling in a tiny trace amount of manganese citrate from a vitamin supplement capsule!