Pseudolyonsite

Chemical formula: Cu₂+₃(V₅+O₄)₂

Pseudolyonsite is a very rare copper vanadate, forming black, tabular crystals in volcanic exhalation environments.

## Characteristics Pseudolyonsite is a mineral from the vanadate group, being a dimorph of lyonsite – it has the same chemical composition but a different crystal structure. It forms very small, thin, tabular or bladed crystals, which usually occur as radial or subparallel aggregates, as well as crusts. Its black color and submetallic luster give it a distinctive appearance, although due to the microscopic size of the crystals, its identification requires specialized equipment. ## Physical Properties This mineral is characterized by a submetallic luster and is opaque. Its calculated density is 4.19 g/cm³. Hardness has not been precisely determined due to the small size and rarity of the crystals. ## Colors and Varieties Pseudolyonsite occurs exclusively in black. No colored varieties or trade names are known. ## History and Name The mineral was first described in 1987 by H.-J. Bernhardt, J. M. Hughes, and G. W. Robinson. Its name refers to its close relationship with lyonsite, of which it is a pseudomorph (dimorph). The type locality, from which the research material originated, is Izalco volcano in El Salvador. ## Applications Due to its extreme rarity and microscopic size, pseudolyonsite has no industrial application. It is solely an object of scientific interest and is valued in advanced collections of rare minerals.

Properties

Luster: Submetallic
Streak: Reddish-brown
Density: 4.19
Cleavage: Perfect on {010}
Transparency: Opaque
Crystal system: Orthorhombic

Diagnostic features

## Identification Identification of pseudolyonsite under amateur conditions is practically impossible. Key indicators are: black color, submetallic luster, tabular crystal form, and most importantly, the environment of occurrence – high-temperature volcanic fumaroles. Certain identification requires advanced analytical methods, such as X-ray diffraction (XRD) or energy-dispersive X-ray spectroscopy (EDS). ## Distinguishing from Similar Minerals Pseudolyonsite is most often confused with lyonsite, from which it is practically impossible to distinguish visually – this requires analysis of the crystal structure (XRD). It can also be confused with other black, microcrystalline minerals found in fumaroles, such as tenorite or hematite. The mineralogical context and co-occurrence with other rare vanadates (e.g., howardevansite) are important diagnostic clues. ## Crystal Forms Pseudolyonsite crystals are thin, tabular (platy) or bladed. They often form fan-shaped, radial, or chaotic aggregates and crusts on volcanic rocks.

Geological environment

## Genesis Pseudolyonsite is a mineral of volcanic origin. It forms through sublimation from hot gases (at temperatures up to 800°C) in active fumaroles, which are volcanic exhalations. ## Mineral Associations This mineral co-occurs with other products of volcanic sublimation, such as lyonsite, howardevansite, shcherbinaite, thenardite, euchlorine, and hematite. ## Localities The most important and confirmed occurrences of this very rare mineral are found in only a few places worldwide. The type locality is Izalco volcano in El Salvador. Another known occurrence, from which most collector specimens originate, is the Tolbachik volcanic complex in Kamchatka, Russia.

Rarity

Very rare

For collectors

## Quality Criteria In the case of a microscopic mineral like pseudolyonsite, the value of a specimen is primarily determined by the abundance and quality of the crystals. Samples with well-formed, sharp crystals forming rich clusters on a small rock matrix are most prized. Co-occurrence with other rare fumarolic minerals is an additional advantage. ## Popular Localities The vast majority of specimens available on the collector's market come from the fumaroles of Tolbachik volcano in Kamchatka, Russia. Material from the type locality, Izalco volcano, is mainly of historical value and is much harder to obtain.

Care and storage

## Cleaning Pseudolyonsite specimens are extremely delicate and usually microscopic in size. They should not be cleaned mechanically or chemically. Only very careful removal of dust with a stream of compressed air from a safe distance is permissible. ## What to Avoid Contact with water, acids, solvents, and other chemicals should be strictly avoided. The mineral, as a product of volcanic sublimation, may be sensitive to changes in humidity. It should be protected from ultrasound, high temperatures, and any shocks or impacts. ## Storage The safest storage method is to place the specimen in a sealed "micromount" box, which protects against dust, mechanical damage, and humidity changes. It should be stored under stable room conditions.

Sources

IMA Mineral List (CNMNC)