Mcbirneyite

Chemical formula: Cu<sup>2+</sup><sub>3</sub>(V<sup>5+</sup>O<sub>4</sub>)<sub>2</sub>

McBirneyite is a very rare copper vanadate, forming microscopic, tabular crystals of an intensely green color.

## Characteristics McBirneyite is a mineral belonging to the vanadate group; chemically, it is a copper(II) vanadate. It occurs as very small, tabular or bladed crystals, which rarely exceed 0.3 mm in length. These crystals often form rosette-like or radial aggregates and clusters. Due to its microscopic size, it is a mineral primarily accessible to specialized collectors. ## Physical Properties McBirneyite crystals exhibit a vitreous luster. They are transparent to translucent. The Mohs hardness is estimated at approximately 3.5, and the density calculated based on the formula and cell parameters is 4.35 g/cm³. ## Colors and Varieties This mineral is characterized by a vibrant, green color. No varieties have been distinguished. ## History and Name McBirneyite was first described in 1986 by Eugene E. Foord and colleagues. The mineral is named in honor of Alexander R. McBirney (1924–2009), a professor of volcanology at the University of Oregon, in recognition of his contributions to the study of Izalco volcano in El Salvador, where the mineral was discovered. ## Uses McBirneyite has no industrial application. Its significance is purely scientific and collectible.

Properties

Mohs hardness
3.5
Luster
Vitreous
Streak
Light green
Density
4.35
Cleavage
Perfect on {010}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Triclinic

Diagnostic features

## Identification Identification of mcbirneyite requires specialized equipment. Recognition is based on microscopic observation of characteristic, green, tabular crystals forming rosette-like aggregates. Final confirmation requires advanced analytical methods, such as X-ray diffraction (XRD) or electron spectroscopy (EDS/WDS). ## Distinguishing from Similar Minerals McBirneyite can be confused with other secondary copper minerals, such as malachite, brochantite, or other rare vanadates (e.g., stoiberite, ziesite). Differentiation with the naked eye is impossible. It differs from malachite by its lack of reaction with hydrochloric acid. It can only be distinguished from other copper vanadates by crystallographic and chemical analysis. ## Crystal Forms Crystals are very small, thin, and tabular, often elongated, with a hexagonal or rhombic outline. They typically form radial aggregates, rosettes, or fan-shaped clusters on the surface of the host rock.

Geological environment

## Genesis McBirneyite is a secondary mineral, formed as a result of volcanic fumarolic activity. It crystallizes from vanadium- and copper-rich volcanic gases at high temperatures in an oxidizing environment. It precipitates as coatings and crusts on the surface of basaltic lava. ## Mineral Associations This mineral co-occurs with other rare products of volcanic exhalations, such as shcherbinaite, stoiberite, ziesite, bannermanite, as well as tenorite and hematite. ## Localities The only confirmed and described locality for mcbirneyite in the world (type locality) is Izalco volcano in the Sonsonate department of El Salvador. It is an endemic mineral to this single location.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of mcbirneyite specimens is primarily assessed based on the richness and aesthetics of the microscopic aggregates. Most valued are specimens with clearly formed, rosette-like clusters of intensely green crystals, contrasting well with the host rock. Crystal size, though always microscopic, is also important – larger and better-formed plates are more desirable. The presence of rare associated minerals is also significant. ## Popular Localities All known mcbirneyite specimens originate exclusively from Izalco volcano in El Salvador. This is the only locality from which this mineral has been obtained.

Care and storage

## Cleaning Specimens containing mcbirneyite should be cleaned very carefully, preferably using compressed air to remove dust. Any contact with water or chemicals is inadvisable due to the microscopic size and potential reactivity of the crystals. Ultrasonic cleaners should be avoided. ## What to Avoid Avoid contact with acids and other chemicals. The mineral is susceptible to abrasion and mechanical damage. It should be protected from high temperatures and humidity. ## Storage It is recommended to store specimens in stable conditions, in sealed containers or display cases, to protect them from dust, humidity, and physical damage. The safest form of storage is specialized micromount boxes.

Sources

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