Koktaite
Chemical formula: (N<sup>3-</sup>H<sub>4</sub>)<sub>2</sub>Ca(S<sup>6+</sup>O<sub>4</sub>)<sub>2</sub>·H<sub>2</sub>O
Koktaite is a rare, colorless or white ammonium calcium sulfate, forming tiny, acicular crystals and efflorescences.
Properties
- Mohs hardness
- 2.5
- Luster
- Vitreous
- Streak
- White
- Density
- 2.14-2.15
- Cleavage
- Perfect on {010}
- Fracture
- Uneven
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Koktaite is identified based on its typical forms of occurrence – fine, acicular crystals forming efflorescences and encrustations. Its formation environment, i.e., dumps and spoil heaps of lignite mines, is also characteristic. Solubility in water is an important diagnostic feature. However, final identification requires advanced analytical methods, such as X-ray diffraction (XRD). ## Distinguishing from Similar Minerals It can be confused with other secondary sulfates found in similar environments, such as gypsum or mascagnite. It differs from gypsum by its much greater delicacy and form of occurrence (it rarely forms such large crystals). From mascagnite, which is ammonium sulfate, it can be distinguished by chemical tests for the presence of calcium. ## Crystal Forms Crystals are very small, acicular or bladed, elongated along one axis. They form radial, fan-shaped aggregates, as well as coatings and crusts on rock surfaces.
Geological environment
## Genesis Koktaite is a secondary mineral, formed as a result of post-mining processes. It forms on dumps and spoil heaps of lignite or coal mines. Its genesis is linked to the reaction of waters percolating through rocks, which leach sulfates (formed from pyrite oxidation) and ammonia (originating from the decomposition of organic matter in coal). These waters, reacting with calcium-bearing rocks (e.g., marls), lead to the crystallization of koktaite under low-temperature conditions. ## Mineral Associations It most commonly co-occurs with gypsum, epsomite, mascagnite, native sulfur, and tschermigite. ## Localities The most important and classic locality is Žeravice in Moravia, Czech Republic. This mineral has also been found in other coal mines, including Pécs in Hungary and several locations in Germany (e.g., Saxony).
Rarity
Very rare
For collectors
## Quality Criteria The collector's appeal of a specimen primarily depends on the richness and abundance of koktaite efflorescences on the rock matrix. Samples with well-visible, dense aggregates of acicular crystals are highly valued. Due to the microscopic size of the crystals, purity and individual forms are not the main criterion. The aesthetics of the entire specimen and the contrast with the substrate are important. ## Popular Localities The most classic and sought-after specimens by collectors come from the type locality - Žeravice in the Czech Republic. Specimens from other confirmed localities, such as Pécs in Hungary, are also valued due to the rarity of the mineral.
Care and storage
## Cleaning Koktaite specimens are extremely delicate and sensitive to water. Mechanical cleaning is not recommended. The safest way to remove dust is with a soft brush or by carefully using a photographic blower bulb. ## What to Avoid Contact with water, which can dissolve or damage the crystals, must be strictly avoided. The mineral is sensitive to moisture, so it should not be stored in humid conditions. It should also be protected from all chemicals and high temperatures. ## Storage It is recommended to store koktaite specimens in sealed, closed containers (so-called "perky boxes") away from sources of moisture and dust. Due to its brittleness, vibrations and shocks should be avoided.