Ammoniotinsleyite

Chemical formula: (N<sup>3-</sup>H<sub>4</sub>)Al<sub>2</sub>(PO<sub>4</sub>)<sub>2</sub>(OH)·2H<sub>2</sub>O

Ammoniotinsleyite is a very rare aluminum ammonium phosphate, forming microscopic, colorless crystals, found in a single locality worldwide.

## Characteristics Ammoniotinsleyite is a hydrated aluminum ammonium phosphate. It occurs as very small, bladed or tabular crystals, rarely exceeding 0.2 mm in length. The crystals are colorless and transparent, often forming rosette-like or radial aggregates. Due to its microscopic size, its visual features are only discernible under high magnification. ## Physical Properties The crystals exhibit a vitreous luster. Hardness and density have not been precisely measured due to the small size of the samples. The mineral is transparent. ## Colors and Varieties Ammoniotinsleyite is colorless. No varieties have been distinguished. ## History and Name The mineral was approved by the IMA in 2022. Its name honors Frank C. Tinsley (born 1945), an American mineral collector and curator, in recognition of his contribution to mineralogy. The name also refers to the presence of ammonium ions (NH₄) in its chemical composition. It was discovered in the Tinsley Mine in Clay County, Texas, USA. ## Uses Ammoniotinsleyite has no commercial or industrial applications. It is of purely scientific and collector's interest as an extremely rare mineral.

Properties

Luster
Vitreous
Streak
White
Cleavage
Perfect on {010}
Transparency
Transparent
Crystal system
Triclinic

Diagnostic features

## Identification Identification of ammoniotinsleyite is impossible without advanced analytical methods, such as Raman spectroscopy or X-ray diffraction (XRD), due to its microscopic size and lack of characteristic visual features. It occurs on a limonite matrix. ## Distinction from Similar Minerals It can be confused with other secondary phosphates occurring in similar parageneses, such as tinsleyite (its potassium analog) or leucophosphite. Differentiation requires specialized chemical analysis to confirm the dominance of the ammonium ion. ## Crystal Forms It forms very small, elongated, bladed crystals, often flattened. These crystals combine into small, radial or rosette-like aggregates on the surface of the host rock.

Geological environment

## Genesis Ammoniotinsleyite is a secondary mineral. It formed as a result of the reaction of phosphate-rich solutions, derived from the decomposition of organic matter (likely bat guano), with aluminum minerals within siderite-limonite concretions. Its formation is associated with mining fires, which influenced the local environmental chemistry. ## Mineral Associations At the type locality, it coexists with tinsleyite, leucophosphite, sphalerite, pyrite, and minerals from the kaolinite group, deposited on a limonite and siderite matrix. ## Localities The only known occurrence of ammoniotinsleyite worldwide is the Tinsley Mine (South-West-Tinsley Mine) in Clay County, Texas, USA. This is its type locality.

Rarity

Extremely rare

For collectors

## Quality Criteria As a "micromount" type mineral, the quality of a specimen is primarily determined by the abundance and development of microscopic crystals within the field of view. Samples with numerous, well-formed, radial crystal aggregates, clearly contrasting with the matrix, are most highly valued. Precise analytical documentation confirming the mineral's identification is also important. ## Popular Localities The Tinsley Mine in Texas, USA, is the sole source of specimens. All samples available on the collector's market originate from this single locality.

Care and storage

## Cleaning Ammoniotinsleyite specimens, due to their extreme rarity and microscopic nature, should not be cleaned under amateur conditions. All treatments should be left to specialists. If absolutely necessary, compressed air (from a safe distance) can be used to remove dust. ## What to Avoid Avoid contact with water, chemicals, ultrasound, and all forms of mechanical cleaning (e.g., brushes). The mineral is likely sensitive to elevated temperatures, which can lead to its dehydration. It should be protected from shocks and vibrations. ## Storage Specimens should be stored exclusively in specialized "micromount" boxes, protecting them from dust, moisture, and mechanical damage. Store in stable temperature conditions and low humidity.

Sources

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