Zýkaite
Chemical formula: Fe<sup>3+</sup><sub>4</sub>(As<sup>5+</sup>O<sub>4</sub>)<sub>3</sub>S<sup>6+</sup>O<sub>4</sub>(OH)·15H<sub>2</sub>O
Zýkaite is a rare, hydrated iron arsenate-sulfate, forming fine, acicular crystals and earthy aggregates of white or yellowish color.
Properties
- Mohs hardness
- 2
- Luster
- Silky
- Streak
- White
- Density
- 2.5
- Cleavage
- Perfect on {010}
- Fracture
- Uneven
- Transparency
- Translucent to opaque
- Crystal system
- Orthorhombic
Diagnostic features
## Identification Zýkaite is difficult to identify without advanced research methods (XRD, EDS). It can be preliminarily recognized by its mode of occurrence – as white or yellowish, earthy, and very porous masses or tiny acicular crystals associated with other arsenates on old mine dumps. ## Distinguishing from Similar Minerals It can be confused with other secondary sulfates and arsenates, such as pharmacosiderite, scorodite, bukovskýite, or pitticite. Differentiation requires chemical analysis. Bukovskýite, often co-occurring with zýkaite, forms more compact, waxy aggregates of a greenish or yellowish-brown color. Pitticite is usually amorphous and has a vitreous or resinous appearance. ## Crystal Forms Crystals are very small, acicular or hair-like, elongated along the [001] axis. They typically form disordered, tangled aggregates, as well as massive, earthy or chalk-like concentrations.
Geological environment
## Genesis Zýkaite is a secondary mineral, forming in the oxidation (weathering) zones of ore deposits rich in arsenic, mainly arsenopyrite. It forms as a result of the reaction of acidic mine waters with primary minerals and surrounding rocks. It is a typical mineral of old mine dumps and spoil heaps environments. ## Mineral Associations It most often co-occurs with arsenopyrite (as a primary mineral), as well as with other secondary arsenates and sulfates, such as bukovskýite, scorodite, pitticite, kankite, gypsum, and jarosite. ## Localities The most important and classic localities for this mineral are in the Czech Republic, from where it was first described. These are the dumps of old mines in the Kaňk area near Kutná Hora and in Safoda near Příbram. It is also known from several other places in the world, including the Tsumeb mine in Namibia and Greece (Lavrion mines).
Rarity
Very rare
For collectors
## Quality Criteria The collecting appeal of zýkaite is limited due to its inconspicuous appearance and microscopic crystals. The most valued specimens are those showing rich, clean clusters of fine needles, contrasting with the color of the host rock. Association with other rare arsenates is also important. Specimens from the type locality (Kaňk, Czech Republic) have higher value for specialist collectors. ## Popular Localities Specimens from the Czech Republic (Kaňk, Příbram), which represent the type material for this mineral, are by far the most sought after by collectors.
Care and storage
## Cleaning Zýkaite specimens are extremely delicate and brittle. They should not be cleaned mechanically or with water. The safest method is to remove dust with a soft brush or a photographic air blower. Contact with water can lead to dissolution or damage to the mineral. ## What to Avoid Contact with water, chemicals, and especially acids, must be strictly avoided. The mineral is sensitive to changes in humidity and temperature. It should not be heated or exposed to direct sunlight. ## Storage Zýkaite requires storage under stable conditions, preferably in a closed, dry container (e.g., a "membrane box") to protect it from mechanical damage and humidity changes. It should be kept away from sources of vibration.