Phoxite

Chemical formula: (N<sup>3-</sup>H<sub>4</sub>)<sub>2</sub>Mg<sub>2</sub>((C<sub>2</sub>)<sup>6+</sup>O<sub>4</sub>)(PO<sub>3</sub>OH)<sub>2</sub>(H<sub>2</sub>O)<sub>4</sub>

Phoxite is an extremely rare, organic magnesium and ammonium phosphate, found in bat guano in caves on the Arabian Peninsula.

## Characteristics Phoxite is a mineral of unusual, organic origin. It forms aggregates of small, platy or acicular crystals, which rarely exceed 1 mm in length. They usually occur as radial aggregates or small, rosette-like groups. Due to its extreme rarity and small crystal size, it is a mineral known primarily in scientific circles. ## Physical Properties Phoxite crystals are very small and brittle. The mineral is characterized by a vitreous luster and is transparent. Its Mohs hardness is approximately 2, making it very soft. The density of phoxite is low, around 2.05 g/cm³. ## Colors and Varieties Phoxite is colorless. No colored varieties or trade names are known. ## History and Name The mineral was first described in 2011 by Stephen J. Mills and his team. The name "phoxite" comes from the combination of two key chemical components: phosphate and oxalate, reflecting its unique chemical composition. It was approved by the International Mineralogical Association (IMA) under number 2010-058. The type locality (locus typicus) is Murubbeh Cave in Umm al-Maradim, Saudi Arabia.

Properties

Mohs hardness
2
Luster
Vitreous
Streak
White
Density
2.05
Cleavage
Good on {010}
Fracture
Uneven
Transparency
Transparent
Crystal system
Monoclinic

Diagnostic features

## Identification Field identification of phoxite is practically impossible. Identification requires advanced laboratory methods, such as X-ray diffraction (XRD) and chemical analysis (EDS/WDS), due to its specific composition and occurrence as microscopic crystals. A key feature is its unique formation environment – bat guano. ## Differentiation from Similar Minerals Phoxite can be confused with other rare phosphates or oxalates found in caves, such as weddellite, whewellite, or archeyite. Differentiating it from these minerals is only possible through detailed chemical and crystallographic analysis. ## Crystal Forms Phoxite forms very small, platy or acicular crystals, elongated along the [100] axis. These crystals often combine into radial or stellate aggregates.

Geological environment

## Genesis Phoxite is a mineral of biogenic origin. It forms under specific conditions as a result of reactions between phosphoric acid and ammonia, derived from the decomposition of bat guano, and oxalic acid, which can be a product of fungal or lichen metabolism. It crystallizes directly on cave walls or within guano deposits. ## Mineral Associations This mineral co-occurs with other minerals formed in cave environments, such as archeyite, bifosfammite, weddellite, gypsum, halite, and newberyite. ## Localities The only confirmed occurrence of phoxite in the world is its type locality – Murubbeh Cave, located in the Umm al-Maradim archipelago in Saudi Arabia.

Rarity

Extremely rare

For collectors

## Quality Criteria Due to its extreme rarity, every phoxite specimen has scientific value. For collectors specializing in rare or systematic minerals, the most important criterion is the analytically confirmed identity of the mineral. Crystal size and quality are of secondary importance, although well-formed aggregates visible under a microscope on a rock matrix are most desirable. ## Popular Localities The only source of specimens is the type locality in Saudi Arabia, which makes the mineral practically unavailable on the collector's market.

Care and storage

## Cleaning Phoxite specimens are extremely delicate and potentially water-soluble. Mechanical cleaning or the use of liquids is absolutely inadvisable. They should be left in their untouched state. ## What to Avoid Avoid contact with water, chemicals, as well as any vibrations and impacts. Changes in temperature and humidity can lead to mineral degradation. It should not be heated or exposed to ultrasound. ## Storage Phoxite must be stored under stable conditions, preferably in a sealed, padded "micromount" container that protects it from physical damage and humidity changes. Storage in a dry environment is crucial for specimen preservation.

Sources

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