Oxammite

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

Oxammite is a rare organic mineral – hydrated ammonium oxalate, occurring as brittle, colorless or white crystals and efflorescences.

## Characteristics Oxammite is a mineral from the group of organic substances, and chemically, hydrated ammonium oxalate. It occurs rarely, forming small, tabular or prismatic crystals, often gathered into radial aggregates or rosettes. It can also be found in granular, earthy masses, as well as efflorescences and coatings. It is a very brittle and soft mineral, and its colorless, white, or yellowish crystals have a vitreous luster. ## Physical Properties Oxammite is characterized by low hardness, measuring 2.5 on the Mohs scale, which means it can be scratched with a fingernail. Its density is also low, approximately 1.5 g/cm³. Crystals exhibit perfect cleavage in one direction. The luster is vitreous, and the mineral can be transparent to translucent. ## Colors and Varieties This mineral is most often colorless, white, or has a straw-yellow hue. No color varieties or commercial varieties are distinguished. ## History and Name The name oxammite comes from its chemical composition – it is a salt of oxalic acid and ammonia. The mineral was first described in 1870 by Charles Upham Shepard based on material found in guano on the Guañape Islands in Peru. ## Uses Oxammite has no industrial application. Its significance is purely scientific and for collectors.

Properties

Mohs hardness
2.5
Luster
Vitreous
Streak
White
Density
1.5
Cleavage
Perfect on {110}
Fracture
Conchoidal
Transparency
Transparent to translucent
Crystal system
Orthorhombic

Diagnostic features

## Identification The key diagnostic feature of oxammite is its very low hardness (2.5) and low density. Its solubility in water is also characteristic. It occurs in a specific environment – in guano deposits or in lake sediments rich in organic matter. It reacts with acids, releasing ammonia. ## Distinguishing from Similar Minerals Oxammite can be confused with other rare organic minerals found in guano, such as whewellite or weddellite. However, whewellite and weddellite (calcium oxalates) are significantly harder (2.5-3) and do not dissolve in water as easily as oxammite. It is distinguished from other soft, white minerals (e.g., gypsum) by its genesis and reaction with water. ## Crystal Forms It forms small, tabular or short-prismatic crystals with a rhombic cross-section. They often occur in the form of radial or stellate aggregates, as well as granular masses and earthy coatings.

Geological environment

## Genesis Oxammite is a mineral of organic origin. It forms as a result of the reaction of oxalic acid and ammonia, which are products of the decomposition of organic matter under specific conditions. Most often, it forms in guano deposits of seabirds or bats, where putrefactive processes rich in nitrogen compounds occur. ## Mineral Associations This mineral co-occurs with other organic minerals and phosphates typical of guano deposits. Its most common associated minerals are sal ammoniac, mascagnite, phosphammite, as well as whewellite and weddellite. ## Localities The most important and historical locality for oxammite is the Guañape Islands off the coast of Peru. It is also known from the Baracoa cave in Cuba. It also occurs in lake sediments near the town of Tadżyk in the Czech Republic.

Rarity

Rare

For collectors

## Quality Criteria Specimens with well-formed, transparent crystals, forming visually attractive, radial aggregates on the matrix, are most valued by collectors. Due to the rarity of the mineral, any specimen from a confirmed locality, even in the form of an efflorescence, has collector's value. Crystal size rarely exceeds a few millimeters, so specimens with larger crystals are exceptionally desirable. ## Popular Localities Classic and most well-known specimens come from the Guañape Islands in Peru. Material from this locality is considered typical for this mineral.

Care and storage

## Cleaning Oxammite specimens are extremely sensitive to water, in which they readily dissolve. Wet cleaning is absolutely forbidden. Only very careful removal of dust with a soft brush or a stream of compressed air from a distance is permissible. ## What to Avoid Avoid all contact with water, water vapor, and other liquids. The mineral is very soft and brittle, susceptible to mechanical damage. It should be protected from high air humidity, which can lead to its slow dissolution and degradation. It should also be protected from high temperatures. ## Storage Oxammite requires storage in conditions of controlled, low humidity. It is best kept in a sealed, closed box (such as a "membrane box" or a box with a desiccant). Avoid exposing it to open air, especially on humid days.

Sources

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