Bartonite

Chemical formula: K₆Fe₂₀S₂₆S

Bartonite is a rare, brownish-black iron and potassium sulfide, forming spindle-shaped crystals in alkaline igneous rocks.

## Characteristics Bartonite is an iron and potassium sulfide, belonging to the bartonite group. It occurs as very small, spindle-shaped or tabular crystals, usually not exceeding 1 mm in length. It most often forms inclusions in other minerals, mainly in bornite and chalcopyrite. It is opaque and has a metallic luster. Its color is characteristic, brownish-black or reddish-brown, which distinguishes it from many other sulfides. ## Physical Properties This mineral is characterized by a Mohs hardness of 3.5, classifying it as a relatively soft mineral. It has a metallic luster and is opaque. Its density is quite high, approximately 4.16 g/cm³. It exhibits weak cleavage in one direction. ## Colors and Varieties Bartonite occurs in uniform colors, from brownish-black to reddish-brown. No color varieties or commercial varieties are known. ## History and Name The mineral is named in honor of Paul B. Barton Jr. (1930-2012), an American geochemist and mineralogist who worked at the United States Geological Survey, for his contributions to sulfide research. Bartonite was first described in 1978 based on material from the Coyote Peak mine in Humboldt County, California, USA. ## Applications Due to its rarity and occurrence as microscopic crystals, bartonite has no industrial applications. It is of purely scientific interest and is an object of interest for collectors specializing in rare minerals and micromounts.

Properties

Mohs hardness: 3.5
Luster: Metallic
Streak: Black
Density: 4.16
Cleavage: Weak on {110}
Fracture: Uneven
Transparency: Opaque
Crystal system: Tetragonal

Diagnostic features

## Identification Bartonite is recognized by its characteristic brownish-black color, metallic luster, and spindle-shaped crystal form. It occurs as inclusions in other sulfides, mainly in bornite. Final identification requires advanced analytical methods, such as electron microprobe analysis (EDS/WDS) or X-ray diffraction (XRD), due to the microscopic size of the crystals. ## Distinguishing from Similar Minerals It can be confused with other dark sulfides, such as djerfisherite, with which it often co-occurs. However, djerfisherite usually has a more greenish or brownish-green hue. It is distinguished from chalcopyrite by its darker color and lack of a brassy-yellow luster. It is distinguished from bornite by the absence of characteristic purple iridescence. ## Crystal Forms Bartonite crystals are typically very small, spindle-shaped or elongated and flattened (tabular). They often form irregular aggregates or clusters embedded in the matrix of other minerals.

Geological environment

## Genesis Bartonite is a mineral of magmatic origin. It forms in the late stages of crystallization in ultramafic, silica-undersaturated rocks, such as kimberlites and carbonatites. It forms under conditions of high sulfur and potassium activity. ## Mineral Associations This mineral most often co-occurs with djerfisherite, chalcopyrite, bornite, pentlandite, troilite, native copper, as well as with platinum-group minerals (PGE). ## Localities The most important and well-documented bartonite localities worldwide include: - Coyote Peak Mine in California, USA (type locality). - Kimberlite deposits in the Republic of South Africa, including the Bultfontein and De Beers mines. - Nickel and copper deposits in the Norilsk region of Siberia, Russia. - Penikat igneous complex in Finland.

Rarity

Very rare

For collectors

## Quality Criteria The quality of bartonite specimens is primarily assessed based on the size and development of the crystals, which is rare. The most valued specimens are those with well-formed, isolated crystals with a distinct luster, contrasting with the surrounding matrix (e.g., with bornite). Due to the microscopic nature of the mineral, the quality of micromount preparation is crucial. ## Popular Localities Specimens from the type locality in California and from kimberlites in South Africa are the most classic examples of this mineral. Material from Russian deposits in the Norilsk region has also provided well-studied samples.

Care and storage

## Cleaning Specimens with bartonite, especially micromounts, should be cleaned very carefully. The safest method is to use compressed air (from a safe distance) to remove dust. Avoid contact with water and chemical agents that may react with sulfides. ## What to Avoid Avoid humid environments, which can lead to oxidation and decomposition of sulfides. The mineral is sensitive to acids. It should not be heated or subjected to ultrasound. ## Storage Specimens should be stored in a dry place, preferably in sealed containers or "micromount" boxes, to protect them from dust, moisture, and mechanical damage. Display should be in enclosed showcases.

Sources

IMA Mineral List (CNMNC)