Famatinite

Chemical formula: Cu¹⁺Cu²⁺₂Sb³⁺S²⁻₄

Famatinit is a rare copper and antimony mineral, forming dark, metallic-lustered crystals, valued by collectors for its origin.

## Characteristics Famatinit is a copper and antimony sulfide, belonging to the stannite group. It rarely forms well-developed crystals, which are usually small and have a pseudo-tetrahedral or pseudo-octahedral habit. Most often, it occurs as granular aggregates, massive forms, or as inclusions in other ore minerals. Its surface is often covered with a patina or weathering products, which can give it a dull appearance or iridescent tarnish. ## Physical Properties This mineral is characterized by a hardness of 3.5 on the Mohs scale and is relatively brittle. It has a metallic luster, which is distinct on fresh surfaces but dulls over time. Its density is approximately 4.5 g/cm³. It is opaque. ## Colors and Varieties Famatinit has a characteristic color ranging from coppery-red, through purplish-gray, to black. The streak is black. No color or commercial varieties are distinguished. ## History and Name The mineral's name comes from its discovery locality – the Sierra de Famatina mountains in La Rioja province, Argentina. It was first described in 1873 by the German mineralogist Alfred Stelzner. ## Uses Due to its rarity and occurrence in small quantities, famatinit has no industrial significance as an ore of copper or antimony. However, it is an object of interest for collectors specializing in rare ore minerals and systematics.

Properties

Mohs hardness
3-4
Color
Deep pinkish brown
Luster
Metallic
Streak
Black
Density
4.635
Cleavage
Good on {101} Distinct on {110}
Fracture
Irregular/Uneven,Conchoidal
Transparency
Opaque
Crystal system
Tetragonal

Diagnostic features

## Identification Famatinit can be identified by its characteristic coppery-red to purplish-gray color, metallic luster, and black streak. It often occurs in association with other copper sulfides, such as enargite, chalcopyrite, or bornite. It is brittle and relatively soft. ## Distinguishing from Similar Minerals It can be confused with enargite, with which it forms a solid solution and often co-occurs. However, enargite has a more grayish-black color and perfect cleavage. Bornite has a similar hue on a fresh fracture but quickly develops a characteristic, iridescent, purplish-blue tarnish. Luzonit, being its polymorph, is practically impossible to distinguish without advanced studies (e.g., XRD). ## Crystal Forms Crystals are rare, usually small, and pseudo-tetrahedral in shape. Most often, it is found as granular aggregates, massive forms, or as small inclusions in other minerals.

Geological environment

## Genesis Famatinit is a hydrothermal mineral. It forms in medium- and low-temperature ore veins. It is a typical component of some copper deposits, especially those rich in arsenic and antimony. ## Mineral Associations It most commonly co-occurs with enargite (with which it forms an isomorphic series), luzonite, tetrahedrite, tennantite, chalcopyrite, pyrite, sphalerite, covellite, barite, and quartz. ## Localities The most important localities worldwide include the historical type locality in Sierra de Famatina, Argentina. Additionally, it occurs in copper mines in Butte, Montana (USA), Tsumeb, Namibia, Bor, Serbia, as well as in the Mankayan region in the Philippines, and in some deposits in Peru (e.g., Quiruvilca, Cerro de Pasco).

Rarity

Rare

For collectors

## Quality Criteria The most prized specimens by collectors are those with well-formed, even if small, crystals with a distinct metallic luster and characteristic color. Color contrasts with associated minerals, such as white barite or quartz, enhance their attractiveness. Specimens from classic, historical localities, such as Famatina or Tsumeb, are particularly sought after. ## Popular Localities Among the most known and valued localities from which collector specimens originate are: Sierra de Famatina (Argentina), Tsumeb (Namibia), Butte (Montana, USA), and Bor (Serbia).

Care and storage

## Cleaning Famatinit specimens should be cleaned very carefully, preferably dry, using a soft brush to remove dust. The use of water, especially with detergents, is not recommended, as it can accelerate oxidation processes and surface dulling. ## What to Avoid Avoid contact with chemicals, acids, and bases, which can react with sulfides. The mineral is sensitive to moisture and temperature changes. It should not be heated or exposed to prolonged sunlight. ## Storage It is recommended to store famatinit in a dry place, preferably in closed collector boxes or display cases, away from direct light and sources of moisture. To prevent oxidation, desiccants can be used.

External references

Sources

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