Djerfisherite

Chemical formula: K₆(Fe,Cu,Ni)₂₅S₂₆Cl

A rare sulfide of potassium, iron, copper, and nickel, found mainly in kimberlites, alkaline pegmatites, and meteorites.

## Characteristics Djerfisherite is a complex sulfide with a metallic luster and a characteristic brown color in various shades. It usually forms small, irregular grains embedded in the host rock. Well-formed crystals are rare and have a cubic habit, which is typical for its isometric crystal system. It is an opaque mineral. ## Physical Properties This mineral has a hardness of 3.5 on the Mohs scale, making it relatively soft. Its density is approximately 4.2 g/cm³. The luster is strongly metallic, and the streak, which is the color of the powdered mineral, is black. It does not exhibit cleavage but may show parting parallel to the {111} octahedron faces. ## Colors and Varieties Its color ranges from bronze-gold and bronzy to greenish-brown. Variations in shades are mainly due to variable copper and nickel content, which can substitute for iron in the crystal structure. There are no named commercial or color varieties. ## History and Name The mineral was first described in 1966 by Louis H. Fuchs. The name djerfisherite was given in honor of Daniel Jerome Fisher (1896–1988), a professor of mineralogy at the University of Chicago. The type specimen is material from the Kota-Kota meteorite, which fell in Malawi. ## Uses Djerfisherite has no industrial applications. However, it is an object of scientific interest and is valued by mineral collectors due to its specific and rare occurrences, such as in meteorites or as inclusions in diamonds.

Properties

Mohs hardness: 3.5
Luster: Metallic
Streak: Black
Density: 4.2
Cleavage: None
Fracture: Conchoidal
Transparency: Opaque
Crystal system: Cubic

Diagnostic features

## Identification Characteristic features of djerfisherite include its bronzy-brown color, strong metallic luster, and black streak. Its occurrence in specific geological environments – kimberlites, alkaline pegmatites, and especially meteorites – is a key diagnostic indicator. If crystals are visible, their cubic form is a distinguishing feature. ## Distinguishing from Similar Minerals It can be confused with other metallic-looking sulfides. It differs from pyrite by its lower hardness and darker, brown color (pyrite is harder and bright yellow). It differs from chalcopyrite by its more brown hue (chalcopyrite is brass-yellow) and usually a different environment of occurrence. Pentlandite has a lighter, pale yellow color. Final confirmation often requires chemical analysis. ## Crystal Forms It most often occurs as anhedral (irregularly formed) grains and aggregates. Rare, well-formed crystals adopt a cubic habit {100}, sometimes with poorly developed {111} octahedron faces.

Geological environment

## Genesis Djerfisherite forms under strongly reducing conditions, with high potassium and sulfur activity. Its genesis is varied. It occurs in kimberlite pipes, where it is sometimes found as an inclusion in diamonds. It is a component of some alkaline pegmatites, nepheline syenites, and carbonatites. It is also a primary mineral in meteorites, especially enstatite chondrites. It has also been found in volcanic exhalation products and in salt domes. ## Mineral Associations Depending on the environment of occurrence, it is associated with various minerals. In meteorites, these include kamacite, troilite, enstatite, and niningerite. In terrestrial rocks (pegmatites, carbonatites), it co-occurs with phlogopite, calcite, apatite, nepheline, sodalite, aenigmatite, and shcherbakovite. In Poland, in the Kłodawa salt dome, it is associated with halite and anhydrite. ## Localities Important localities worldwide include alkaline massifs on the Kola Peninsula in Russia (Khibiny, Kovdor), where well-formed crystals are found. Numerous occurrences have been reported in kimberlite pipes in Yakutia (Russia). Other known localities include the Hicks Dome volcanic complex in Illinois (USA) and the type meteorite locality – Kota-Kota (Malawi). This mineral has also been found in Poland in the Zechstein Kłodawa salt dome.

Rarity

Rare

For collectors

## Quality Criteria The most important criterion for evaluating a specimen is the degree of crystal development and size. Sharp, well-defined cubes are much more valuable than irregular grains. Specimens in which djerfisherite is embedded in a rare host rock, e.g., as an inclusion in a diamond or as part of a meteorite, are also highly prized. Purity and intensity of color also contribute to attractiveness. ## Popular Localities The most sought-after specimens by collectors, characterized by the best crystal development, come from alkaline pegmatites of the Khibiny and Kovdor massifs on the Kola Peninsula in Russia.

Care and storage

## Cleaning Dry cleaning with a soft brush or compressed air is recommended to remove dust. Due to the possibility of oxidation, contact with water should be avoided. If necessary, distilled water should be used, and the specimen should be dried immediately and thoroughly. ## What to Avoid High humidity should be avoided, as it can lead to slow decomposition of the mineral. Djerfisherite is sensitive to acids. As a relatively soft mineral, it is susceptible to scratching, so it should be protected from contact with harder minerals. ## Storage Djerfisherite specimens are best stored in a dry place, in sealed containers or display cases. It is advisable to consider using desiccants (e.g., silica gel) to ensure stable conditions and minimize the risk of oxidation.

External references

https://en.wikipedia.org/wiki/https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FDjerfisherite