Vajdakite

Chemical formula: (Mo<sup>6+</sup>O<sub>2</sub>)<sub>2</sub>As<sup>3+</sup><sub>2</sub>O<sub>5</sub>·3H<sub>2</sub>O

Vajdakite is a very rare, hydrated molybdenum oxoarsenate, forming microscopic, acicular crystals of an intensely orange-red color.

## Characteristics Vajdakite is a hydrated molybdenum oxoarsenate, occurring as extremely small, acicular or bladed crystals. It typically forms radial aggregates or crusts. Its most characteristic feature is its intense, orange-red to red color, which distinguishes it from the host rock. The crystals are transparent and exhibit a strong, vitreous luster. ## Physical Properties This mineral is very soft, with a Mohs hardness of approximately 2. It is also very light, and its crystals are brittle. It exhibits perfect cleavage in one direction. The luster is described as vitreous. ## Colors and Varieties Vajdakite occurs in a characteristic, uniform color from orange-red to red. No color varieties or commercial varieties are known. ## History and Name The mineral was discovered in the Geschieber uranium mine in Jáchymov, Czech Republic, and described in 1999. Its name honors Josef Vajdak (born 1934), a Czech mineral collector who specialized in minerals from Jáchymov and was the first to find this mineral. ## Uses Due to its extreme rarity and microscopic size, vajdakite has no industrial applications. It is solely an object of scientific and collecting interest for specialized collectors of rare minerals and micromounts.

Properties

Mohs hardness
2
Luster
Vitreous
Streak
Light yellow
Density
3.65
Cleavage
Perfect on {010}
Fracture
Uneven
Transparency
Transparent
Crystal system
Monoclinic

Diagnostic features

## Identification Vajdakite is primarily recognizable by its unique combination of features: intense orange-red color, acicular or bladed crystal habit forming radial aggregates, and occurrence in a very specific geological environment. Due to its microscopic size, a stereoscopic microscope is essential for its identification. ## Distinguishing from similar minerals It can be confused with other rare, secondary arsenates or molybdates of similar color, such as wulfenite or mimetite. However, the characteristic acicular habit and mineral associations in Jáchymov are key to its differentiation. Final confirmation requires advanced analytical methods, such as Raman spectroscopy or X-ray diffraction. ## Crystal forms Vajdakite crystals are elongated, acicular or bladed, often flattened. They usually occur as radial or tangled aggregates, as well as fine crusts on the host rock.

Geological environment

## Genesis Vajdakite is a secondary mineral, formed in the oxidation zones of polymetallic deposits rich in arsenic and molybdenum. It forms as a result of the weathering of primary ore minerals under low temperature and pressure conditions. ## Mineral associations In its type locality (Jáchymov), vajdakite co-occurs with other rare secondary minerals such as betpakdalite-NaCa, čejkaite, melkovite, moprobit, natropharmacosiderite, gypsum, and quartz. ## Localities The only confirmed locality for vajdakite in the world is the Geschieber uranium mine in Jáchymov, in the Karlovy Vary region of the Czech Republic. This is its type locality.

Rarity

Extremely rare

For collectors

## Quality criteria The quality of vajdakite specimens is primarily assessed based on the richness and aesthetics of the crystal aggregates. Most valued are specimens with clearly formed, radial groups of acicular crystals of an intense, orange-red color. The contrast with the rock matrix and the absence of damage to the delicate crystals are also important. Due to the microscopic nature of the mineral, the size of individual crystals is rarely the main criterion. ## Popular localities The only source of vajdakite specimens is its type locality - the Geschieber mine in Jáchymov, Czech Republic. All specimens available on the collector's market originate from this single location.

Care and storage

## Cleaning Specimens of vajdakite should be handled with the utmost care. Cleaning is highly inadvisable due to the extreme fragility and small size of the crystals. If absolutely necessary, compressed air can be used from a safe distance to remove loose dust particles. Any contact with water or other liquids should be avoided. ## What to avoid Contact with water, chemicals, ultrasound, and sudden temperature changes must be strictly avoided. The mineral is very soft and brittle, so it must be protected from any impacts, abrasions, and vibrations. It should not be exposed to direct sunlight. ## Storage Vajdakite specimens, typically in the form of micromounts, should be stored exclusively in specialized, sealed perky boxes that protect them from dust, moisture, and mechanical damage. Store in stable room conditions, away from sources of heat and light.

Sources

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