Rebulite
Chemical formula: Tl<sup>1+</sup><sub>5</sub>Sb<sup>3+</sup><sub>5</sub>As<sup>3+</sup><sub>8</sub>S<sup>2-</sup><sub>22</sub>
Rebulite is a very rare thallium, antimony, and arsenic sulfosalt, forming black, metallic crystals, found mainly in North Macedonia.
Properties
- Mohs hardness
- 2-2.5
- Luster
- Metallic
- Streak
- Red-brown
- Density
- 5.1
- Cleavage
- Good on {100}
- Fracture
- Uneven
- Transparency
- Opaque
- Crystal system
- Monoclinic
Diagnostic features
## Identification Characteristic features of rebulite include its black color, strong metallic luster, and reddish-brown streak. High density combined with low hardness is also an important indicator. However, a key diagnostic element is its paragenesis – co-occurrence with other rare thallium sulfosalts in known localities. ## Distinguishing from Similar Minerals Rebulite can be confused with other black, metallic sulfosalts, such as stibnite, cylindrite, or other minerals from the Tl-As-Sb group. It is distinguished from stibnite by its reddish-brown streak (stibnite has a grayish-black streak). However, definitive identification is extremely difficult without advanced analytical methods, such as X-ray microanalysis (EDS/WDS), which allows for the determination of its unique chemical composition. ## Crystal Forms Rebulite crystallizes in columnar, prismatic, or acicular forms, often elongated along one axis. These crystals usually form disordered aggregates or are embedded in the host rock (most commonly in dolomite or calcite).
Geological environment
## Genesis Rebulite is a low-temperature hydrothermal mineral. It forms under unique geochemical conditions, characterized by high concentrations of thallium, arsenic, and antimony, and low sulfur content. ## Mineral Associations This mineral occurs in association with other rare sulfosalts. Its most common associations include lorandite, vrbaite, raguinite, getchellite, orpiment, and realgar. It also co-occurs with calcite and dolomite, which constitute the host rock. ## Localities The most important and historically first occurrence of rebulite is the polymetallic deposit of Allchar (Alšar), located near the town of Majdan in North Macedonia. This is the classic and most well-known locality for this mineral, from which most research and collection material originates.
Rarity
Very rare
For collectors
## Quality Criteria The collectible value of rebulite is primarily determined by its extreme rarity. The most prized specimens are those that display well-formed, even if small, crystals with a distinct luster. An additional advantage is a rich association with other rare minerals from this locality, such as lorandite or vrbaite. Due to the nature of its occurrence, specimens are usually micromounts or small rock samples with mineral inclusions. ## Popular Localities Virtually all rebulite specimens available on the collector's market come from its type locality – the Allchar deposit in North Macedonia. This is a classic locality for thallium mineralogy.
Care and storage
## Cleaning Rebulite specimens should only be cleaned mechanically, using a soft brush to remove dust. Wet cleaning should be avoided. If absolutely necessary, a small amount of distilled water can be used, followed by immediate and thorough drying of the specimen. ## What to Avoid **Warning: The mineral is highly toxic due to its high thallium and arsenic content.** Inhaling dust that may arise during handling must be strictly avoided. Hands should be thoroughly washed after each contact with the specimen. It must not be heated or exposed to acids and other chemicals. It is very soft and brittle, so it must be protected from impacts, scratching, and vibrations. ## Storage It is recommended to store specimens in airtight, sealed containers (e.g., "membrane box" type) to reduce the risk of dusting and accidental contact. Each container must be clearly labeled as toxic material. It should be kept away from children, pets, and food.