Tetrahedrite
Chemical formula: (Cu,Fe)₁₂Sb₄S₁₃
Tetrahedrite is a sulfosalt mineral, an important ore of copper and antimony, often forming characteristic tetrahedral crystals.
Description
## Characteristics Tetrahedrite is a copper-antimony sulfosalt, often containing admixtures of iron, zinc, and sometimes silver. Typical specimens are crystals with a tetrahedral habit, hence the mineral's name. The surface of the crystals can be granular or massive. The color of tetrahedrite is usually steel-gray to black, often with a metallic luster. ## Physical Properties The hardness of tetrahedrite on the Mohs scale ranges from 3 to 4, making it a relatively soft mineral. It has a metallic luster, and its streak is usually black to reddish-brown. It is opaque. The density of tetrahedrite ranges from 4.6 to 5.2 g/cm³, depending on its chemical composition, especially its silver content. ## Colors and Varieties Tetrahedrite occurs mainly in steel-gray to black colors. A variety containing a significant amount of silver, called freibergite, is known and is a valuable silver ore. Other varieties may contain admixtures of mercury (schwatzite) or zinc. ## History and Name The name tetrahedrite comes from the Greek word "tetraedron," referring to the characteristic shape of its crystals. The mineral was first described in the 19th century, and its importance as a metal ore was quickly recognized. ## Uses Tetrahedrite is an important ore of copper and antimony. Varieties rich in silver (freibergite) also constitute a valuable silver ore. It is sought after by collectors due to its characteristic crystals.
Diagnostic features
## Identification Tetrahedrite can be identified by its characteristic tetrahedral crystal habit, metallic luster, and steel-gray to black color. The mineral's streak is black to reddish-brown. It is relatively soft, which can be checked with a hardness test. ## Distinguishing from Similar Minerals Tetrahedrite can be confused with other sulfosalts of similar color and luster, such as tennantite, with which it forms an isomorphic series. Differences often require chemical analysis. It can also be confused with galena, but galena has perfect cleavage, which tetrahedrite lacks, and lower hardness. ## Crystal Forms Typical crystal forms of tetrahedrite are tetrahedra, often with well-developed faces. Crystals can be single or form twins. It also occurs as massive, granular, or crusty aggregates.
Geological environment
## Genesis Tetrahedrite forms in hydrothermal ore veins, often in association with other sulfides and sulfosalts. It is a typical mineral of medium- and low-temperature hydrothermal deposits. It also occurs in some contact-metasomatic deposits. ## Mineral Associations Tetrahedrite often co-occurs with other ore minerals such as chalcopyrite, pyrite, galena, sphalerite, argentite, as well as with quartz, calcite, and barite. ## Localities Important tetrahedrite localities include Freiberg in Germany, Banská Štiavnica in Slovakia, Cavnic in Romania, Butte in Montana (USA), as well as in Peru, Bolivia, and Mexico.
Rarity
Not very common
Collector aspects
## Quality Criteria The most prized tetrahedrite specimens are well-formed, distinct tetrahedral crystals with intense color and strong metallic luster. Large, undamaged crystals on a matrix are particularly sought after. Clarity and lack of inclusions also increase the value of a specimen. ## Popular Localities The most valued tetrahedrite specimens come from classic localities such as Freiberg (Germany), Banská Štiavnica (Slovakia), and Cavnic (Romania), as well as from mining regions in Peru and Bolivia, where large and aesthetic crystals are found.
Care and storage
## Cleaning Tetrahedrite is a relatively soft mineral, so it should be cleaned carefully. It is best to use a soft brush or a cotton cloth moistened with water. Avoid strong rubbing to prevent scratching the surface. ## What to Avoid Avoid contact with acids and strong chemicals, which can damage the mineral's surface. Tetrahedrite is sensitive to high temperatures, which can cause oxidation and discoloration. Prolonged exposure to direct sunlight is also not recommended. ## Storage Tetrahedrite specimens are best stored in enclosed display cases or boxes, away from dust and moisture. Due to its softness, avoid storing it with harder minerals that could scratch it.