Valleriite

Chemical formula: ₂[(Fe₃+,Cu₁+)S₂-]·₁.₅₃[(Mg,Al)(OH)₂]

This is a rare sulfide mineral with an unusual, layered structure, characterized by very low hardness and a brownish-yellow color.

## Characteristics Valleriite is a sulfide group mineral distinguished by a complex, layered chemical structure, in which iron and copper sulfide packets alternate with magnesium and aluminum hydroxide packets. It is extremely soft and flexible, feeling greasy or waxy to the touch. It most commonly occurs as small scales, flakes, fibrous or radial aggregates, and also as earthy masses. It rarely forms visible, hexagonal crystals. ## Physical Properties It is characterized by a very low Mohs hardness of only 1-1.5, meaning it can be scratched with a fingernail. It is opaque, with a density of 3.14 g/cm³. The mineral's flakes are flexible but inelastic. It exhibits perfect cleavage in one direction, which facilitates its separation into thin plates. ## Colors and Varieties Its color is usually brownish-yellow, brown, or close to brown, often with a metallic luster. Sometimes it is described as dark gray. No named varieties are distinguished. ## History and Name The mineral was first described in 1870. Its name comes from the Swedish chemist and mineralogist Johan Gottschalk Wallerius (also known as Johan Waller), who lived from 1709-1785. The type locality, from which the first studied specimens originated, is the Aurora mine in Kaveltorp, Örebro region, Sweden. ## Uses Due to its rarity and small accumulations, valleriite has no industrial significance. It is solely an object of interest for collectors of rare minerals and scientists studying complex crystalline structures.

Properties

Mohs hardness: 1-1.5
Luster: Metallic
Streak: Black
Density: 3.14
Cleavage: <mi>{0001}</mi>
Fracture: Micaceous
Transparency: Opaque
Crystal system: Trigonal

Diagnostic features

## Identification Key diagnostic features of valleriite include its extremely low hardness (1-1.5 on the Mohs scale), brownish-yellow color, perfect cleavage in one direction, and a characteristic greasy or waxy feel to the touch. The streak is black. The mineral's flakes are flexible. ## Distinguishing from Similar Minerals It can be confused with graphite, molybdenite, or pyrrhotite. It differs from graphite and molybdenite primarily by its brownish-yellow color (those are gray to black). It differs from pyrrhotite by significantly lower hardness and flexibility of the flakes. Unlike magnetic pyrrhotite, valleriite does not exhibit magnetism. ## Crystal Forms It most often forms scaly, platy, or fibrous aggregates. Crystals, if present, are small, tabular hexagons. It is often found in radial clusters or as thin veins and coatings on other minerals.

Geological environment

## Genesis Valleriite is a hydrothermal mineral, forming at relatively low temperatures. It forms within ultramafic rocks (e.g., dunites, peridotites) and mafic rocks (e.g., gabbros) that have undergone serpentinization processes. It can also occur in copper and nickel sulfide deposits. ## Mineral Associations It co-occurs with minerals such as chalcopyrite, cubanite, pentlandite, pyrrhotite, troilite, mackinawite, as well as minerals from the serpentine and chlorite groups. ## Localities Important localities worldwide include the Bushveld Complex in South Africa (known for large accumulations), Sudbury in Canada, the Duluth Complex in Minnesota (USA), and nickel deposits in the Pechenga region on the Kola Peninsula in Russia. It also occurs at its type locality in Kaveltorp, Sweden.

Rarity

Rare

For collectors

## Quality Criteria For collectors, the most desirable specimens are those with well-formed, though usually microscopic, hexagonal crystals. Rich, scaly or fibrous aggregates with an intense, brownish-yellow color, clearly contrasting with the host rock, are also valued. Due to the mineral's rarity, every well-identified specimen has collector's value. ## Popular Localities The best collector's specimens, often of considerable size, come from the platinum-bearing horizons of the Bushveld Complex in South Africa. Significant finds have also been reported in Sudbury, Canada, and in some mines in the USA.

Care and storage

## Cleaning Valleriite specimens are extremely delicate and soft. Any mechanical cleaning, including the use of brushes, should be avoided. Only very careful blowing with compressed air from a safe distance to remove dust is permissible. ## What to Avoid The mineral is sensitive to acids and other chemicals. It should be protected from scratching, impacts, and abrasion. Due to its flaky and flexible nature, it is easily subject to permanent deformation and mechanical damage. ## Storage Specimens should be stored only in closed display boxes, away from harder minerals that could scratch them. It is not suitable for open display due to its fragility and susceptibility to dirt.