Rohaite
Chemical formula: (Tl,Pb,K)₂Cu₈.₇Sb₂S₄
Rohaite is a rare, black sulfide containing thallium, lead, potassium, copper, and antimony, discovered in Greenland.
Properties
- Mohs hardness
- 3-3.5
- Luster
- Metallic
- Density
- 0
- Transparency
- Opaque
- Crystal system
- Orthorhombic
Diagnostic features
## Identification Identification of rohaite is possible only through advanced laboratory methods, such as chemical composition analysis (EDS) and X-ray diffraction (XRD). In collecting conditions, identification relies on knowledge of associated minerals and origin from the type locality. ## Distinguishing from Similar Minerals It can be confused with other rare, black sulfides found in the Ilímaussaq complex, such as cuprostibite or roquesite. Definitive differentiation requires specialized chemical analysis, especially due to the presence of thallium, which is a diagnostic feature. ## Crystal Forms Rohaite forms very small, lath-like or acicular crystals, usually not exceeding 0.2 mm in length. These crystals often occur in irregular aggregates or as inclusions in other minerals, mainly chkalovite.
Geological environment
## Genesis Rohaite forms under hydrothermal conditions within nepheline syenites and their pegmatites. It is a product of a late stage of crystallization in an environment rich in rare elements, such as thallium. ## Mineral Associations This mineral is associated with other rare minerals from the Ilímaussaq complex. It is most commonly found in association with chkalovite (in which it forms inclusions), as well as aegirine, analcime, microcline, nepheline, natrolite, sorensenite, sphalerite, galena, cuprostibite, and roquesite. ## Localities The only confirmed locality of rohaite in the world is its type locality: the Kuannersuit (Kvanefjeld) plateau in the Ilímaussaq alkaline complex, in the Kujalleq region of southern Greenland.
Rarity
Extremely rare
For collectors
## Quality Criteria The quality of a rohaite specimen is determined by the abundance and size of microscopic crystals within the host rock. The most valued samples are those in which rohaite aggregates are clearly visible under a microscope and well-formed. Association with other rare minerals from this locality is also important. ## Popular Localities All collectible specimens come from a single location in the world – the Kuannersuit plateau in Greenland. This is a classic locality for many rare minerals, and material from there is highly prized by collectors specializing in microminerals and rare-element minerals.
Care and storage
## Cleaning Rohaite specimens, typically microscopic inclusions, do not require cleaning. Any attempts at mechanical or chemical cleaning of the host rock can irreversibly damage the delicate crystals. ## What to Avoid Avoid contact with chemicals, ultrasonics, and any abrasive agents. The mineral is soft and brittle, so it should be protected from impacts and scratches. ## Storage Specimens containing rohaite should be stored in stable conditions, in specialized "micromount" boxes that protect them from dust, moisture, and mechanical damage. Avoid exposure to direct sunlight and extreme temperatures.