Barite tumbled stones from Greenland.

The mineral barite (also called barium sulphate, heavy spar, blanc fixe or permanent white) is a barium sulphate with the chemical formula BaSO4. It has a hardness of 3 to 3.5. Barite is not soluble in water and has a high resistance to other chemicals. It has a density of 4.48 kg/dm3, a white stripe color and the cleavage of the mineral is perfect according to [210] and imperfect according to [010]. The birefringence of barite is 0.0110 - 0.0120. There are stones made of impure barium sulphate that glow in the dark, so-called Bologna stones. Barite usually occurs in hydrothermal veins where it forms at low to medium temperatures. Furthermore, it is found in tunnels and cavities in limestone and in newly formed, moist and slightly saline soils. In Belgium, barite is found in Blieberg, Angleur, Villers-en-Fagne and Fleurus.