Krausite

Chemical formula: KFe<sup>3+</sup>(S<sup>6+</sup>O<sub>4</sub>)<sub>2</sub>·H<sub>2</sub>O

Krausite is a rare, brittle potassium iron sulfate, forming characteristic short prismatic crystals of an intense yellow color.

## Characteristics Krausite is a hydrated potassium iron sulfate, known for forming well-developed, short prismatic crystals. Typical specimens have an intense, lemon-yellow to greenish-yellow color and a vitreous luster. This mineral is brittle and often occurs as aggregates of small, radial or spherulitic clusters on host rocks. ## Physical Properties Krausite is characterized by a relatively low hardness of about 2.5 on the Mohs scale, meaning it can be scratched with a fingernail. It has a vitreous luster and is transparent to translucent. Its density is approximately 2.84 g/cm³. It is soluble in water. ## Colors and Varieties This mineral occurs in shades from pale yellow and lemon-yellow to greenish-yellow. No named varieties are distinguished, and its color is quite consistent and characteristic. ## History and Name Krausite was first described in 1933 by William F. Foshag based on specimens found in Calico Hills, California, USA. The mineral is named in honor of Edward Henry Kraus (1875-1973), professor of mineralogy at the University of Michigan and dean of its College of Pharmacy. ## Uses Due to its rarity, brittleness, and water solubility, krausite has no industrial applications. It is solely a mineral of scientific and collector's interest.

Properties

Mohs hardness
2.5
Luster
Vitreous
Streak
Pale yellow
Density
2.835-2.843
Cleavage
Good on {010}
Fracture
Conchoidal
Transparency
Transparent to translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Krausite can be identified by its characteristic, intense yellow color, vitreous luster, and typical short prismatic crystals. Key diagnostic features include its low hardness (approx. 2.5) and water solubility. The reaction to moisture is one of the simplest tests. ## Distinguishing from Similar Minerals It can be confused with other secondary yellow sulfates such as jarosite or copiapite. However, jarosite is harder (2.5-3.5) and does not dissolve in water. Copiapite often forms coatings and crusts, less commonly well-formed crystals, and has a different chemical composition. The water solubility test is the best way to distinguish krausite. ## Crystal Forms It forms short, prismatic crystals with a cross-section resembling a square or rectangle, often terminated by flat pinacoids. It also occurs as radial aggregates, spherulites, and granular and fibrous clusters.

Geological environment

## Genesis Krausite is a secondary mineral, formed by the evaporation of sulfate-rich solutions. It forms in desert and arid conditions, in the oxidation zones of sulfide deposits, and also as a product of volcanic exhalations (fumaroles). ## Mineral Associations It often co-occurs with other sulfates and evaporite minerals, such as thenardite, alunogen, voltaite, copiapite, metavoltine, as well as native sulfur, gypsum, and halite. ## Localities The most important and classic locality, from which the best specimens originate, is Calico Hills in San Bernardino County, California, USA. It is also known from the Boron mine (California), the Chuquicamata mine in Chile, Mount Vesuvius in Italy, and several localities in Iran and China.

Rarity

Rare

For collectors

## Quality Criteria The most prized krausite specimens are those with well-formed, sharp crystals of intense, lemon-yellow color and good transparency. Contrast with the rock matrix and crystal size are important – the larger and more distinct, the more valuable the specimen. Radial aggregates with a silky luster are also attractive. ## Popular Localities Specimens from the historic locality in Calico Hills, California, are by far the most sought after by collectors. They are characterized by classic crystal habit and set the standard for this mineral.

Care and storage

## Cleaning Krausite is soluble in water, so it must absolutely not be cleaned wet. To remove dust, only a very soft brush or compressed air from a distance and at low pressure should be used. ## What to Avoid Avoid all contact with water, water vapor, and other liquids that can dissolve or damage the mineral. It should be protected from high humidity, which can lead to its degradation. Also, avoid shocks and impacts due to its brittleness. ## Storage Krausite specimens should be stored in a dry place, preferably in a tightly sealed container (e.g., a display box) with a desiccant (e.g., silica gel). Display should be in a closed cabinet, away from sources of moisture and sudden temperature changes.

Sources

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