Carnallite
A variety of Minerals
What is Carnallite?
Carnallite (also carnalite) is an evaporite mineral, a hydrated potassium magnesium chloride with formula KMgCl3·6(H2O). It is variably colored yellow to white, reddish, and sometimes colorless or blue. It is usually massive to fibrous with rare pseudohexagonal orthorhombic crystals. The mineral is deliquescent (absorbs moisture from the surrounding air) and specimens must be stored in an airtight container. Carnallite occurs with a sequence of potassium and magnesium evaporite minerals: sylvite, kainite, picromerite, polyhalite, and kieserite. Carnallite is an uncommon double chloride mineral that only forms under specific environmental conditions in an evaporating sea or sedimentary basin. It is mined for both potassium and magnesium and occurs in the evaporite deposits of Carlsbad, New Mexico; the Paradox Basin in Colorado and Utah; Stassfurt, Germany; the Perm Basin, Russia; and the Williston Basin in Saskatchewan, Canada. These deposits date from the Devonian through the Permian Periods. In contrast, both Israel and Jordan produce potash from the Dead Sea by using evaporation pans to further concentrate the brine until carnallite precipitates, dredging the carnallite from the pans, and processing to remove the magnesium chloride from the potassium chloride. Carnallite was first described in 1856 from its type location of Stassfurt Deposit, Saxony-Anhalt, Germany. It was named for the Prussian mining engineer Rudolf von Carnall (1804–1874).
Uses & Applications
Carnallite is mostly used in fertilizers. It is an important source of potash. Only sylvite outranks carnallite's importance in potash production. Both are uncommon because they are some of the last evaporites to form. Soluble potassium salts are the main sources for fertilizer. This is because the potassium is difficult to separate from insoluble potassium feldspar. Carnallite is a minor source of magnesium worldwide; however, it is Russia's main source.
Market Value Factors
Pricing varies for every rock and mineral, so use these universal factors to gauge Carnallite before comparing listings or appraisals.
Size & Weight
Larger, intact specimens usually command higher prices.
Rarity & Demand
Scarce material or popular varieties sell at a premium.
Condition & Finish
Chips, repairs, and heavy wear lower value; clean prep helps.
Treatment & Provenance
Untreated specimens with documented locality are prized.
Carnallite Localities Map
See where Carnallite is found with a localities map, collecting zones, and geology context. Generate a sample map preview below.
Key Characteristics
Characteristics of Carnallite
Carnallite's refractive index ranges from 1.467 to 1.494. Carnallite may be red as a result of hematite (Fe2O3) inclusions. The fragmented shards of iron oxide produce red tints in the thin laminae of hematite. Carnallite is also deliquescent in high humidity. This implies that it is also extremely soluble in water. Individual crystals are pseudo-hexagonal and tabular but are extremely rarely seen. Field indicators of carnallite are environment of formation, absence of cleavage, and fracture. Other indicators can be density, taste, associations to local minerals, and whether it is capable of luminescence. Carnallite has a bitter taste. Carnallite may not only be fluorescent but is capable of being phosphorescent. The potassium that carnallite contains fuses easily within a flame, creating a violet color.
Formation of Carnallite
Halides are binary compounds. They are composed of a halogen and a metal ion. The crystal chemistry of halides is characterized by the electronegativity of halogen ions. This means that the dominant large ions are the Cl, Br, F, or I. These are easily polarized. The ions combine with similarly large but low valence and weakly polarized cations. The cations are mostly of the alkali metal group. Sylvite is a binary compound with the formula KCl. Sylvite precipitates first from mixed solutions of K, Mg and Cl, leaving a brine enriched in magnesium from which the mixed halide carnallite then precipitates.
Composition of Carnallite
Carnallite's chemical formula is KMgCl3·6(H2O). Synthetic carnallite crystal specimens can be produced from 1.5 mole percent KCl and 98.5 mole percent MgCl2·6H2O by slow crystallization at 25 °C. Its density is 1.602 g/cm. Carnallite can also be produced by grinding the combination of hydrated magnesium chloride and potassium chloride.
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Quick Facts
Physical Properties
- Color
- Yellow to white, reddish, seldom white, colourless or blue.
- Hardness (Mohs)
- 2.5
- Density
- 1.598 g/cm³
- Streak
- White
Chemical Properties
- Chemical Formula
- KMgCl3 · 6H2O
- Elements
- Cl, H, K, Mg, O
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Carnallite FAQs
How do I identify Carnallite?
Carnallite can be identified by its hardness of 2.5 on the Mohs scale, Yellow to white color. Look for these key characteristics when examining specimens.
What color is Carnallite?
Carnallite typically appears in Yellow to white, reddish, seldom white, colourless or blue.. Color can vary depending on impurities and formation conditions.
How hard is Carnallite?
Carnallite has a hardness of 2.5 on the Mohs scale. This makes it a soft mineral that can be scratched easily.
What is the characteristics of carnallite of Carnallite?
Carnallite's refractive index ranges from 1.467 to 1.494. Carnallite may be red as a result of hematite (Fe2O3) inclusions. The fragmented shards of iron oxide produce red tints in the thin laminae of hematite. Carnallite is also deliquescent in high humidity. This implies that it is also extremely soluble in water. Individual crystals are pseudo-hexagonal and tabular but are extremely rarely seen. Field indicators of carnallite are environment of formation, absence of cleavage, and fracture. Other indicators can be density, taste, associations to local minerals, and whether it is capable of luminescence. Carnallite has a bitter taste. Carnallite may not only be fluorescent but is capable of being phosphorescent. The potassium that carnallite contains fuses easily within a flame, creating a violet color.
What is the formation of carnallite of Carnallite?
Halides are binary compounds. They are composed of a halogen and a metal ion. The crystal chemistry of halides is characterized by the electronegativity of halogen ions. This means that the dominant large ions are the Cl, Br, F, or I. These are easily polarized. The ions combine with similarly large but low valence and weakly polarized cations. The cations are mostly of the alkali metal group. Sylvite is a binary compound with the formula KCl. Sylvite precipitates first from mixed solutions of K, Mg and Cl, leaving a brine enriched in magnesium from which the mixed halide carnallite then precipitates.
What is the composition of carnallite of Carnallite?
Carnallite's chemical formula is KMgCl3·6(H2O). Synthetic carnallite crystal specimens can be produced from 1.5 mole percent KCl and 98.5 mole percent MgCl2·6H2O by slow crystallization at 25 °C. Its density is 1.602 g/cm. Carnallite can also be produced by grinding the combination of hydrated magnesium chloride and potassium chloride.
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