Ferrotochilinite

Chemical formula: ₆Fe₂+S₂-·₅Fe₂+(OH)₂

Ferrotochlinite is a rare sulfide and hydroxide mineral, forming characteristic cylindrical or tubular crystals of a brownish-black color.

## Characteristics Ferrotochlinite is a sulfide group mineral that also contains hydroxide layers in its structure. Its most characteristic feature is the formation of unusual, cylindrical or tubular crystals, often coiled into spiral or spherical aggregates. Individual crystals are usually microscopic in size. The mineral is opaque, with a color ranging from brown to black. ## Physical Properties Ferrotochlinite is very soft, with a Mohs hardness of only 1. It is a flexible mineral, and its thin lamellae are elastic. It has a density of approximately 3.36 g/cm³. It exhibits a metallic or submetallic luster. It is strongly magnetic. ## History and Name The name "ferrotochlinite" refers to its chemical composition – a high iron content (Latin: *ferrum*) – and its structural similarity to tochlinite. The mineral was first described in 1971. ## Applications Due to its rarity and microscopic crystal sizes, ferrotochlinite has no industrial applications. It is solely an object of scientific and collecting interest.

Properties

Mohs hardness: 1
Luster: Metallic
Streak: Black
Density: 3.36
Cleavage: Perfect on {001}
Fracture: Uneven
Transparency: Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification The key diagnostic feature of ferrotochlinite is its unique morphology in the form of cylindrical, coiled crystals and aggregates. Other important features include very low hardness (1 on the Mohs scale), brownish-black color, metallic luster, and strong magnetism. ## Distinguishing from Similar Minerals It can be confused with graphite or molybdenite due to its low hardness and dark color, but the characteristic cylindrical crystal form and strong magnetism allow for its unambiguous differentiation. Unlike graphite, it is much denser and magnetic. ## Crystal Forms It forms unique, cylindrical or tubular crystals that often coil, creating spiral, tubular, or spherulitic (spherical) aggregates. Less commonly, it occurs as fibrous masses or lamellar crusts.

Geological environment

## Genesis Ferrotochlinite is a low-temperature hydrothermal mineral. It forms in serpentinites, often as a result of the alteration of iron and magnesium sulfides in the presence of water. It can also crystallize in some meteorites (carbonaceous chondrites). ## Mineral Associations It most commonly co-occurs with minerals from the serpentine group (antigorite, lizardite), magnetite, pyrrhotite, pentlandite, chalcopyrite, cubanite, mackinawite, and valleriite. ## Localities The most important occurrences of this mineral are in Russia, including the Kola Peninsula (Kovdor massif) and the Urals. It is also known from Canada (Ontario, Quebec), USA (California), Finland, Germany, and from occurrences in meteorites, e.g., in the Orgueil carbonaceous chondrite, which fell in France.

Rarity

Very rare

For collectors

## Quality Criteria The most prized specimens by collectors are those with well-formed, macroscopic cylindrical or spherulitic aggregates on a contrasting rock matrix. The quality of the specimen depends on the size and preservation of these fragile structures. Due to the microscopic nature of most occurrences, any specimen with distinct forms is considered valuable. ## Popular Localities Specimens from the Kovdor massif on the Kola Peninsula in Russia are considered the best in the world. Classic examples of this mineral with well-developed, spherical aggregates originate from there.

Care and storage

## Cleaning Ferrotochlinite specimens are extremely delicate and sensitive. They should not be cleaned mechanically or chemically. Any attempts at cleaning, even with water, can lead to the destruction of the fragile and soft crystals. ## What to Avoid Contact with any moisture, acids, and other chemicals should be avoided. The mineral is unstable under oxidizing conditions and can decompose. It should be protected from temperature changes and direct sunlight. ## Storage It is recommended to store specimens in sealed, dry containers, preferably under stable temperature conditions. Due to its fragility, it should be protected from shocks and vibrations.

Sources

IMA Mineral List (CNMNC)