Tochilinite
Chemical formula: 6(Fe<sup>2+</sup><sub>0.9</sub>S<sup>2-</sup>)·5[(Mg,Fe<sup>2+</sup>)(OH)<sub>2</sub>]
Tochilinite is a rare sulfide and hydroxide mineral, forming characteristic brownish-black, fibrous or cylindrical aggregates with a metallic luster.
Properties
- Mohs hardness
- 1
- Luster
- Metallic
- Streak
- Black
- Density
- 3.06-3.17
- Cleavage
- Perfect on {001}
- Fracture
- Uneven
- Transparency
- Opaque
- Crystal system
- Triclinic
Diagnostic features
## Identification Tochilinite is relatively easy to identify based on its unique morphology – black, coiled, cylindrical or tubular aggregates with a metallic luster. Its extreme softness and flexibility of fibers are also characteristic. ## Distinguishing from Similar Minerals It can be confused with graphite or pyrolusite; however, graphite is more slippery to the touch and leaves a dark streak on paper, while pyrolusite forms harder, dendritic or radiating aggregates. The unique, coiled form of the fibers is a key distinguishing feature of tochilinite. ## Crystal Forms Crystals are extremely rare and appear as small, thin plates. Most often, it occurs as fibrous, cylindrical or tubular aggregates, which can be coiled into spirals. It also forms spherical and radiating aggregates.
Geological environment
## Genesis Tochilinite is a low-temperature hydrothermal mineral. It forms during the serpentinization of ultramafic rocks (peridotites, dunites), where it replaces sulfide minerals such as pentlandite and pyrrhotite. It can also crystallize in voids and fractures within serpentinites. ## Mineral Associations It most commonly co-occurs with minerals from the serpentine group (antigorite, lizardite, chrysotile), awaruite, chalcopyrite, cubanite, magnetite, pentlandite, pyrrhotite, troilite, and valleriite. ## Localities The most important occurrences of this mineral are in Russia, at its discovery site in the Tochil River region of Siberia, and in nickel deposits on the Kola Peninsula. It is also known from the Muskox mine in the Northwest Territories, Canada, from several locations in California and Oregon (USA), as well as from Japan and Italy.
Rarity
Rare
For collectors
## Quality Criteria The most valued specimens by collectors are those with well-developed, distinct, coiled or cylindrical aggregates that have not disintegrated. The contrast with the surrounding host rock (matrix), most often serpentinite, is important. Large, undamaged aggregates are rare and fetch higher prices. ## Popular Localities Specimens from the type locality in Russia and from the Muskox mine in Canada are considered classic and most desired by collectors.
Care and storage
## Cleaning Tochilinite specimens are extremely delicate and sensitive. Wet cleaning should be avoided. Only very careful dust removal with a soft brush or a stream of compressed air from a distance is permissible. ## What to Avoid The mineral is very sensitive to moisture and oxidation – contact with water or chemicals leads to its rapid decomposition. It should be protected from high temperatures, direct sunlight, and changes in humidity. It must not be cleaned in ultrasonic cleaners. ## Storage It is recommended to store specimens in tightly sealed, dry containers (e.g., "perky box" type) away from sources of moisture and light. Due to its fragility, it should be stored separately to avoid mechanical damage.