Sylvite Composition,
Crystallization and Structure

Composition. Potassium chloride, KC1 = Chlorine 47.6, potassium 52.4. Sometimes contains sodium chloride.

Crystallization. Isometric. Cube and octahedron frequently in combination.

Structure. Usually. Cube in granular crystalline masses showing cubic cleavage; compact.

Physical Properties. Perfect cubical cleavage. H. = 2. G. = 1.9. Transparent when pure, yellow or red from impurities. Readily soluble in water. Salty taste but more bitter than in the case of halite.

Test. easily fusible at 1.5, giving violet flame of potassium, which may be obscured by yellow flame due to sodium present. The yellow sodium flame may be filtered out by used of a blue gals, and the violet of the potassium rendered visible. After intense ignition, residue gives alkaline reaction on moistened test paper. Readily soluble in water; solution made acid with nitric acid gives with silver nitrate a heavy precipitate of silver chloride. Distinguished form halite by the violet flame color of potassium and its slightly bitter taste.

Occurrence. Has the same origin, mode of occurrence and associations as halite (which see) but is much more rare. Found in some quantity and at times well crystallized in connection with the salt deposits at Stassfurt, Prussia; from Kalusz in Galicia, etc.

Name. potassium chloride is the sal digestivus sylvii of early chemistry, whence the name for the species.

Use. One source of potassium compounds which are extensively used as fertilizers. Other potassium minerals that are found in Germany in sufficient amount to make them valuable as sources of potassium salts are, carnallite, KC1.MgC12.6H2O (see page 186); kainite, MgSO4.KC13H2O; polyhalite, K2SO4.MgSO4.- 2CaSO4. 2H2O.