Agardite-(Y)

Chemical formula: Cu<sup>2+</sup><sub>6</sub>Y(As<sup>5+</sup>O<sub>4</sub>)<sub>3</sub>(OH)<sub>6</sub>·3H<sub>2</sub>O

Agardite-(Y) is a rare copper and yttrium arsenate, forming characteristic acicular crystals of a vivid blue-green color.

## Characteristics Agardite-(Y) is a mineral belonging to the agardite group, in which yttrium is the dominant rare earth element. It forms very characteristic, slender, acicular crystals that often arrange themselves into radial aggregates, resembling fans, tufts, or rosettes. Specimens are usually small, but their intense color makes them easily noticeable. It is most commonly found as delicate, fibrous crusts on the host rock. ## Physical Properties The Mohs hardness of agardite-(Y) is 3-4, making it a relatively soft and brittle mineral. It has a vitreous luster, and in the case of fibrous aggregates, a silky luster. It is a translucent mineral, and its density is approximately 3.7 g/cm³. ## Colors and Varieties This mineral occurs in various shades of green and blue. The most common colors range from yellowish-green, through emerald-green, to bluish-green. The intensity and hue depend on impurities and specific crystallization conditions. No commercial varieties are distinguished. ## History and Name The name "agardite" was given in 1969 in honor of the French geologist Jules Agard. The suffix "-(Y)" indicates the dominance of yttrium in its chemical structure, distinguishing it from other minerals in this group, such as agardite-(Ce) or agardite-(La). It was discovered in the Bou-Skour mine in Morocco. ## Applications Agardite-(Y) has no industrial applications. Due to its attractive forms and vivid colors, it is a valued and sought-after collector's mineral.

Properties

Mohs hardness
3-4
Luster
Vitreous to Silky
Streak
Pale green
Density
3.72
Cleavage
Good on {1010}
Fracture
Conchoidal
Transparency
Translucent
Crystal system
Hexagonal

Diagnostic features

## Identification The most important diagnostic feature of agardite-(Y) is its habit – it almost always occurs as thin, acicular crystals forming radial aggregates. Its intense, blue-green color and occurrence in association with other secondary copper minerals are also characteristic. ## Distinguishing from Similar Minerals Agardite-(Y) can be confused with other acicular copper minerals. It is distinguished from fibrous malachite by its lack of reaction with hydrochloric acid (malachite effervesces violently). It is distinguished from brochantite and linarite by chemical tests. Final distinction from other minerals of the agardite group (e.g., agardite-(Ce)) is only possible using advanced chemical analyses (e.g., EDS). ## Crystal Forms Crystals are hexagonal, developed as very thin, elongated needles. They almost always form aggregates: radial rosettes, fans, tufts, as well as fibrous and felt-like crusts.

Geological environment

## Genesis Agardite-(Y) is a secondary mineral, formed in the oxidation (weathering) zones of hydrothermal ore deposits. It crystallizes as a result of the reaction of solutions rich in copper, arsenic, and yttrium with primary minerals. Its presence requires a specific geochemical environment where all necessary components are available. ## Mineral Associations It most often co-occurs with other secondary minerals of the oxidation zone, such as malachite, azurite, chrysocolla, pharmacosiderite, goethite, and also with quartz. ## Localities Key and most famous localities worldwide include: - Bou-Skour Mine in Morocco (type locality). - Clara Mine in the Black Forest, Germany. - Laurion (Lavrion) mining district in Greece. - Cornwall in the United Kingdom. - United States (numerous occurrences in Arizona and Utah).

Rarity

Rare

For collectors

## Quality Criteria The most highly valued agardite-(Y) specimens are characterized by an intense, vivid color, from blue-green to emerald. The crystal form is crucial – well-formed, undamaged, radial aggregates with a distinct structure are sought after. Large, rich crusts on a contrasting rock matrix significantly increase the collector's value of the specimen. Purity, meaning the absence of mechanical damage and undesirable coatings, is also an important factor. ## Popular Localities Although the type locality is Morocco, the Clara Mine in Germany and the mines in Greek Laurion are considered classic and provide specimens of the highest quality. Specimens from these locations are particularly sought after by collectors due to their excellent crystal development and color intensity.

Care and storage

## Cleaning Agardite-(Y) is a very delicate and brittle mineral. It should only be dry-cleaned, using a soft brush to remove dust. If necessary, compressed air can be used from a safe distance. Due to its brittleness and solubility, contact with water, especially hot water, is not recommended. Ultrasonic cleaners are absolutely forbidden. ## What to Avoid Avoid contact with all chemicals, especially acids, which can damage it. As an arsenate, it is potentially toxic – avoid inhaling dust and wash hands after each contact with the specimen. The mineral is sensitive to impact and abrasion. Prolonged exposure to strong sunlight can cause color fading. ## Storage Agardite-(Y) specimens are best stored in separate, padded boxes (such as "membrane boxes" or with foam) to protect the delicate needles from mechanical damage. It should be kept in stable conditions, away from moisture and direct sunlight.

External references

Sources

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