• Chemistry: KCl, Potassium Chloride
  • Class: Halides
  • Uses: As a major source of potash and as mineral specimens.
  • Specimens

Sylvite, also called sylvine, is a major source of potassium or potash used in fertilizer products. So great is the need for potassium that sylvite deposits are considered very valuable economically. As a mineral specimen sylvite does not get much attention. The crystals can be well formed and are often reddish due to inclusions of hematite. However, sylvite is very soluble in water and specimens need to be stored in closed containers because even the moisture in the air can degrade its appearance. Never clean a sylvite specimen with water!

Sylvite is closely related to the more common halite, NaCl, and they share so many properties that identification is sometimes difficult. Sylvite commonly has octahedral faces truncating the corners of the cubic crystals. So does halite, but this characteristic is much more prevalent in sylvite than in halite. Better tests include a taste test in which halite, salt, will taste salty and sylvite tastes bitter. This test is good if you need to distinguish one or two specimens, but what if you are testing hundreds of feet of core samples for beds of sylvite verses halite. A good test in those cases is the knife test in which a knife blade when scratched across the surface of the sample will produce a powder in halite and not in sylvite.

There is a low-sodium version of table salt (light salt) which is half halite and half sylvite. Naturally, it has half the sodium content of ordinary table salt, since that sodium has been replaced with potassium. It is a perfectly acceptable substitute for many people, while others consider it bitter.

The name sylvite is easily confused with the much more valuable sylvanite. Sylvanite is a silver gold telluride, AuAgTe4 and should never be mistaken for sylvite.


  • Color is colorless or white, sometimes tinted red, blue or yellow.
  • Luster is vitreous.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is isometric; 4/m bar 3 2/m.
  • Crystal Habits are cubes with frequent octahedral faces truncating the corners of the cube, crystals will often have a cavernous appearance from dissolution. More commonly massive and granular.
  • Cleavage is good in three directions forming cubes.
  • Fracture is uneven.
  • Hardness is 2 - 2.5
  • Specific Gravity is 1.99 (light, surprisingly slightly less dense than halite with a 2.17 specific gravity)
  • Streak is white.
  • Other Characteristics: Dissolves easily in water, does not powder when the blade of a knife is scratched across its surface and has a distinctive bitter taste.
  • Associated Minerals include halite, carnallite, kieserite, gypsum, anhydrite and other evaporite minerals.
  • Notable Occurrences include Strassfurt, Germany; Kalush, Russia; New Mexico, Texas and Kern Co., California, USA; Saskatchewan, Canada; France, Mt. Vesuvius, Italy and Spain.
  • Best Field Indicators are bitter taste, associations and crystal habit.
SYLVITE specimens:
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SYLVITE specimen syv-1
$ 20.00
Dims: 2.81" x 2.31" x 1.5"(7.1 x 5.9 x 3.8 cm)
Wt: 3.38 oz.(96.0 g)
Niland, Salton Sea, Imperial County, California, U.S.A.
I have been told that the color of this cluster of Sylvite crystals is actually caused by hematite inclusions. The cluster has crystals that range in size from 3/8"(9 mm) to 3/4"(1.9 cm) along an edge. These crystals occur in three habits: cubes, octahedrons, and octahedrons that are truncated with cubic faces replacing their points. There are also a variety of crystals that are warped beyond recognition, and some massive Sylvite. There is no host rock, but it was stored for a short period of time on an eiderdown-like substance in moist air, because some of these fibers are stuck to its underside. The crystals have a greasy luster to them and are partially transparent, with considerable cloudiness.
no photo
syv-1 ($ 20.00)
Niland, Salton Sea, Imperial County, California, U.S.A.
SYLVITE specimen syv-2
$ 15.00
Dims: 2.75" x 2.25" x 1.75"(7.0 x 5.7 x 4.4 cm)
Wt: 3.02 oz.(85.6 g)
Niland, Salton Sea, Imperial County, California, U.S.A.
The dominating habit of this cluster is one that resembles pebbly formations of snow with an orange color. There are some cubic crystals present on one edge of the piece; these measure a maximum of 1/2"(1.3 cm) along an edge and show considerable clarity. They have a pearly luster and look almost as if they have been oiled. It does have considerable damage that is confined to one area on the specimen that doesn't have crystalline tendencies. It is a pretty specimen.
no photo
syv-2 ($ 15.00)
Niland, Salton Sea, Imperial County, California, U.S.A.
SYLVITE specimen syv-3
$ 25.00
Dims: 1.8 x 1.4 x 1.2" (4.6 x 3.6 x 3.0 cm)
Wt: 1.4 oz. (39.2 g)
Carlsbad Potash District, Eddy County, New Mexico, U.S.A.
This small hand specimen consists of a heavily broken cluster of intersecting Sylvite cubes. The specimen is obviously a piece out of a larger semicrystalline mass, and though there are no complete crystals present, there are many definable edges and a few clean faces that possess a bright vitreous luster. The specimen is generally translucent, but there are areas of transparence and impressive clarity. Studying one of these shows that the Sylvite is generally colorless, but is heavily included with a brick-red substance that is probably hematite or limonite; this inclusion gives the specimen its generally rusty-red color.
no photo
syv-3 ($ 25.00)
Carlsbad Potash District, Eddy County, New Mexico, U.S.A.


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