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Octahedral Sylvite Crystals

The Mineral sylvite

Sylvite is an economically important mineral and is extensively mined, though it is rarely represented in mineral collections as attractive specimens. It is the most significant form of potash, or potassium-bearing compounds, and has many industrial uses.

Sylvite is very similar to Halite, and is ismorphous with it, but it has a more bitter taste an greater solubility. It sometimes forms as a contrasting accessory mineral to deeply colored Halite specimens. Sylvite is named after named after François Sylvius de le Boe (1614-1672), a Dutch chemist and physician.
Chemical Formula KCl
Composition Potassium chloride
Color Colorless, white, light yellow. Often red or orange from Hematite inclusions.
Streak White
Hardness 2 - 2.5
Crystal System Isometric
Crystal Forms
and Aggregates
Octahedral and cubic with modified octahedral faces. Less commonly cubic. Also in groups of octahedral or cubic crystals, grainy, massive, compact, and fibrous.
Transparency Transparent to translucent
Specific Gravity 2.0
Luster Vitreous
Cleavage 1,all sides
Fracture Conchoidal
Tenacity Brittle
Other ID Marks 1) Strong, bitter taste.
2) Highly soluble in water, especially warm water.
In Group Halides
Striking Features Bitter taste and low hardness
Environment Evaporite deposits such as dry lakes and saline lake shorelines, sedimentary salt beds, and volcanic fumaroles.
Rock Type Igneous, Sedimentary
Popularity (1-4) 3
Prevalence (1-3) 1
Demand (1-3) 2


 -  A mixture of Sylvite and Halite.

Sylvite is the main source of potash, which is an important ingredient in fertilizers. It has other important industrial uses, including aluminium recycling, metal electroplating, and in oil drilling fluids. It is the chief ingredient of potassium supplements, which are used to treat or prevent low potassium conditions such as hypokalemia.

Sylvite was first discovered in very small crystals in the volcanic fumaroles of Mt. Vesuvius, Naples Province, Italy. Other important European localities include Muntanya de Sal (Salt Mountain), Cardona, Catalonia, Spain; and the Boulby Mine, Loftus, Yorkshive, England. In Germany, good Sylvite has been found at Wathlingen, Lower Saxony; Stassfurt, Saxony-Anhalt; and at the Hattorf Potash Works, Werra valley, Hesse.

In the U.S., the two most important deposits of Sylvite are the Carlsbad Potash District, Eddy Co., New Mexico; and Niland, near the Salton Sea, Imperial Co., California. Some of the world's largest deposits of Sylvite are in Canada in the province of Saskatchewan, especially at Esterhazy and Rocanville.

Halite, Hematite, Carnallite, Gypsum, Anhydrite

Halite - Saltier and less bitter than Sylvite, usually forms in cubic crystals whereas Sylivte forms in octahedral crystals.

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