Ammonioleucite
Chemical formula: (N<sup>3-</sup>H<sub>4</sub>)AlSi<sub>2</sub>O<sub>6</sub>
Ammonioleucite is a rare tectosilicate from the zeolite group, an ammonium analogue of leucite, found in organic sediments.
Properties
- Mohs hardness
- 5.5-6
- Luster
- Vitreous
- Streak
- White
- Density
- 2.29
- Cleavage
- None
- Fracture
- Conchoidal
- Transparency
- Transparent to translucent
- Crystal system
- Tetragonal
Diagnostic features
## Identification Identification of ammonioleucite is impossible without advanced analytical techniques. It requires the use of methods such as X-ray diffraction (XRD) to confirm the crystal structure and chemical analysis (e.g., EDS/WDS) to demonstrate the presence of nitrogen (in the form of an ammonium ion), aluminum, and silicon. The characteristic crystal form (trapezohedron) observed under a scanning electron microscope (SEM) is a strong diagnostic indicator. ## Distinguishing from similar minerals Ammonioleucite is visually indistinguishable from leucite and analcime, which form crystals of the same shape. Differentiation requires chemical analysis to identify the dominant cation (NH₄⁺ for ammonioleucite, K⁺ for leucite, Na⁺ for analcime). ## Crystal forms It forms microscopic, well-formed crystals with a trapezohedral habit {211}, typical for minerals of the leucite group. Crystals rarely exceed a size of several tens of micrometers.
Geological environment
## Genesis Ammonioleucite is a low-temperature mineral, forming in the late stages of diagenetic processes or as a result of weak metamorphism in sediments rich in organic matter. The presence of the ammonium ion (NH₄⁺) is directly related to the decomposition of this matter. It forms in voids and fractures in sedimentary rocks, such as shales and sandstones. ## Mineral associations It often co-occurs with other authigenic minerals, such as quartz, calcite, dolomite, pyrite, and also with other zeolites, including ammonium heulandite. ## Localities The most important and best-documented localities are in Japan, particularly in rock formations on the islands of Honshu (e.g., Tsuruoka mine in Oita Prefecture) and Hokkaido. This mineral has also been identified in sediments in the United States (Wyoming) and Russia.
Rarity
Very rare
For collectors
## Quality criteria Ammonioleucite is a mineral of interest mainly to collectors specializing in rare species and micromounts. The value of a specimen is determined by the quality and size of the microcrystals, their abundance on the rock matrix, and confirmation of identification through analysis. The most desirable specimens are those with sharp, well-defined crystals visible under a microscope. ## Popular localities The most prized specimens, which are also type material, come from localities in Japan, especially from the Tsuruoka mine in Oita Prefecture.
Care and storage
## Cleaning Due to their microscopic size and rarity, ammonioleucite specimens typically do not require cleaning and are stored in the condition in which they were found, often in containers protecting them from contaminants. ## What to avoid Avoid contact with strong acids and bases, which can damage the mineral's structure. Heating can lead to the decomposition of the ammonium ion and loss of water, which permanently alters the mineral. It should be protected from moisture and contaminants. ## Storage Specimens, especially those with well-formed microcrystals, should be stored in sealed, stable containers (so-called micromount boxes) to protect them from mechanical damage and dust. Store in a dry place with a stable temperature.