Arsenogoyazite

Chemical formula: SrAl₃(As₅+O₄)(As₅+O₃OH)(OH)₆

Arsenogoyazite is a rare arsenate mineral from the alunite supergroup, forming small, colorless to pale yellow crystals.

## Characteristics Arsenogoyazite is the arsenate analog of goyazite and belongs to the alunite supergroup. It occurs as very small, tabular or pseudocubic crystals, rarely exceeding 0.5 mm. Crystals are typically aggregated into rosette-like or spherical forms. Due to their small size, its visual features are difficult to observe without magnification. ## Physical Properties Arsenogoyazite crystals exhibit a vitreous luster. The Mohs hardness is approximately 4. The mineral is brittle and has perfect cleavage in one direction. It is a relatively dense mineral, which is typical for arsenates. ## Colors and Varieties Arsenogoyazite is most commonly colorless, white, pale yellow, or yellowish-green. No varieties have been distinguished. ## History and Name The mineral's name refers to its chemical composition (dominance of arsenic) and its structural similarity to goyazite. It was first described by Walenta and Dunn

Properties

Mohs hardness: 4
Luster: Vitreous
Streak: White
Density: 3.33
Cleavage: Perfect on {0001}
Fracture: Uneven
Transparency: Transparent to Translucent
Crystal system: Trigonal

Diagnostic features

## Identification Identification of arsenogoyazite is possible almost exclusively using advanced analytical methods, such as Raman spectroscopy or X-ray diffraction (XRD) combined with chemical analysis (EDS/WDS). Visual identification in the field or even in a collection is practically impossible due to the small size of the crystals and similarity to many other secondary minerals. ## Distinguishing from Similar Minerals It can be confused with other minerals from the alunite group, such as arsenogorceixite, goyazite, philipsbornite, or segnitite. Differentiation requires confirmation of chemical composition, particularly the dominance of strontium (Sr) over other large cations (Ba, Pb, Ca) and arsenic (As) over phosphorus (P) and sulfur (S). ## Crystal Forms It mainly forms small, tabular crystals with a trigonal or hexagonal outline, as well as pseudocubic and rhombohedral crystals. It often occurs in the form of rosette-like or spherulitic aggregates.

Geological environment

## Genesis Arsenogoyazite is a secondary mineral, forming in the oxidation (weathering) zones of ore deposits rich in arsenic, especially in the presence of rocks containing aluminum and strontium. It forms as a result of the alteration of primary arsenides and sulfarsenides. ## Mineral Associations It co-occurs with other secondary arsenates and minerals of the oxidation zone. It is most commonly associated with olivenite, quartz, pharmacosiderite, beudantite, segnitite, arsenogorceixite, agardite, and adamite. ## Localities The most important and best-documented localities worldwide are the Clara Mine in the Black Forest (Germany), which is the type locality, and the Cap Garonne Mine in Var (France). It is also known from small occurrences in the Tsumeb Mine (Namibia) and Sterling Hill (New Jersey, USA).

Rarity

Very rare

For collectors

## Quality Criteria As a "micromount" mineral, the value of a specimen is primarily determined by the quality and development of crystals visible under a microscope. Well-defined, sharp crystals forming aesthetic aggregates, set on a contrasting rock matrix, are most prized. Color, though subtle, also matters – specimens with a distinct, yellowish hue are more sought after than colorless ones. Association with other rare minerals is also key. ## Popular Localities Specimens from the Clara Mine in Germany are by far the most valued and sought after by collectors. Material from Cap Garonne in France is also significant from a historical and scientific point of view.

Care and storage

## Cleaning Due to the extreme rarity and small size of the crystals, mechanical cleaning is not recommended. If absolutely necessary, compressed air can be used to remove dust. Avoid contact with water and chemicals. ## What to Avoid Avoid all acids and strong bases, which can react with arsenates. The mineral is brittle, so it should be protected from impacts and vibrations. It should not be heated or subjected to ultrasonic cleaning. ## Storage Arsenogoyazite specimens should be stored under stable conditions, in a sealed "micromount" box, protecting them from dust and mechanical damage. Keep it away from moisture.

Sources

IMA Mineral List (CNMNC)