Trigodomeykite
Chemical formula: Cu<sub>3</sub>As
Trigodomeykite is a rare copper arsenide that crystallizes in the trigonal system, unlike similar minerals.
Properties
- Mohs hardness
- 3-3.5
- Luster
- Metallic
- Streak
- Greyish-black
- Density
- 8.09-8.11
- Cleavage
- None
- Fracture
- Uneven
- Transparency
- Opaque
- Crystal system
- Trigonal
Diagnostic features
## Identification Identifying trigodomeykite is difficult without specialized equipment. It can be preliminarily recognized by its metallic luster, high density, and white or steel-gray color on a fresh fracture. Rapid tarnishing of the surface is also characteristic. Definitive identification requires chemical analysis (EDS) and X-ray diffraction (XRD). ## Distinguishing from Similar Minerals Trigodomeykite is very similar to other copper arsenides, such as domeykite and algodonite. Distinguishing them based on visual characteristics is practically impossible. The key diagnostic feature, from which its name is derived, is its trigonal crystallographic system, whereas domeykite crystallizes in the isometric system. Algodonite has similar properties but a different copper-to-arsenic ratio. ## Crystal Forms Trigodomeykite crystals are extremely rare and microscopic in size. It usually forms massive, granular, or compact aggregates in association with other minerals.
Geological environment
## Genesis Trigodomeykite is a hydrothermal mineral. It forms in ore veins, typically as a result of mineralization processes associated with magmatic activity. It occurs in association with other copper arsenides and sulfides. ## Mineral Associations This mineral often co-occurs with other copper arsenides, such as domeykite and algodonite. At its type locality (Brazil), it was found in association with quartz, chalcopyrite, bornite, covellite, chalcocite, native arsenic, native silver, kutnohorite, and annabergite. ## Localities Beyond its discovery site in the Córrego da Panela mine in Brazil, trigodomeykite has been confirmed in only a few localities worldwide. One important locality is the Talmessi mine in Iran, known for the occurrence of rare arsenides. It has also been reported in the Svornost mine in Jáchymov, Czech Republic.
Rarity
Extremely rare
For collectors
## Quality Criteria As an extremely rare mineral, every analytically confirmed specimen of trigodomeykite is valuable to specialized collectors. The most desirable specimens are those rich in the mineral, with clearly visible, unoxidized areas exhibiting a metallic luster. Specimens with visible, even microscopic, crystals would be of exceptional value. A well-documented locality is also important. ## Popular Localities The most classic and sought-after locality is the type locality – the Córrego da Panela mine in Brazil. Specimens from the Talmessi mine in Iran are also highly prized by collectors specializing in rare minerals.
Care and storage
## Cleaning Due to its rarity and potential fragility, mechanical cleaning is not recommended. If necessary, compressed air can be used to remove dust. Avoid contact with water and chemicals. ## What to Avoid Avoid contact with water, acids, and other chemicals that may react with copper arsenides. The mineral is susceptible to oxidation, so it should be protected from humid air, which accelerates its tarnishing. Due to its arsenic content, avoid inhaling dust during any potential processing. ## Storage Trigodomeykite specimens are best stored in dry conditions, in sealed containers or display cases with controlled humidity, to minimize the oxidation process and preserve their natural luster. It is recommended to store them away from other minerals that could scratch them.