Tetrahedrite
Copper antimony sulfosalt ((Cu,Fe)12Sb4S13)
A gray copper-antimony sulfosalt of the fahlore group, an important ore of copper and often silver, forming tetrahedral crystals.
- Mohs hardness
- 3-4.5
- Color
- Steel-gray to iron-black, metallic
- Type
- mineral
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Overview
Tetrahedrite is a copper antimony sulfosalt, (Cu,Fe)12Sb4S13, and the antimony-dominant member of the fahlore group (it forms a series with arsenic-dominant tennantite). It crystallizes in the cubic system and is named for its characteristic tetrahedral crystal shape.
It is a steel-gray to iron-black metallic mineral and an important ore of copper. Many specimens also carry significant silver, zinc, mercury, and other metals substituting in the structure; the silver-rich variety is called freibergite.
Tetrahedrite is widespread in hydrothermal ore veins and is valued both as an ore and as a collector mineral when in well-formed crystals.
Formation & geology
Tetrahedrite forms in hydrothermal ore veins over a wide range of temperatures, crystallizing from metal-rich fluids in association with other copper, lead, zinc, and silver minerals.
It commonly occurs with chalcopyrite, galena, sphalerite, pyrite, and silver sulfosalts in polymetallic vein and replacement deposits.
Notable localities include the silver-copper districts of Peru and Bolivia, the Erzgebirge of Germany (Freiberg, the source of silver-rich freibergite), Romania, the Cornwall and Devon mines of England, and various deposits in the western United States. Fine sharp tetrahedral crystals come especially from Peru.
How to identify it
Tetrahedrite is identified by its steel-gray to iron-black color, metallic luster, and diagnostic tetrahedral crystal form when crystals are present. Its streak is black to brownish-black, and it has a hardness of 3 to 4.5.
The tetrahedral habit is the strongest clue and helps separate it from similar gray sulfides. Without crystals, it can resemble other gray ores and may require chemical testing to distinguish from tennantite (its arsenic analog) and from galena (which is denser and cleaves cubically).
Mercury- or silver-rich varieties and association with chalcopyrite and silver minerals are useful contextual indicators.
Uses & significance
Tetrahedrite is an important ore of copper and, in silver-rich varieties like freibergite, a significant ore of silver. It can also be a source of antimony, and historically its byproduct metals added to the value of polymetallic ores.
Copper from such ores is used in wiring, plumbing, alloys, and electronics, while recovered silver serves jewelry, coinage, and industry.
For collectors, sharp tetrahedral crystals, particularly lustrous specimens from Peru, are highly desirable. It contains antimony and sometimes arsenic or mercury, so specimens should be handled sensibly and not powdered or ingested.
Frequently asked questions
What is fahlore?
Fahlore is the group name for the tetrahedrite-tennantite series of gray copper sulfosalts; tetrahedrite is the antimony-rich member and tennantite the arsenic-rich one.
Does tetrahedrite contain silver?
Often yes; silver commonly substitutes into the structure, and the silver-rich variety freibergite is an important silver ore.
How do I recognize tetrahedrite?
Look for steel-gray to black metallic material, ideally showing tetrahedral crystals, with a black streak and association with other sulfide ores.
What metals are extracted from tetrahedrite?
Primarily copper, frequently silver, and sometimes antimony, depending on the composition of the particular deposit.
Tetrahedrite guides
In-depth guides for identifying, valuing, and understanding Tetrahedrite.
