Schertelite

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

Schertelite is a very rare hydrated ammonium magnesium phosphate, forming colorless, pearly crystals in caves with bat guano.

## Characteristics Schertelite is a mineral from the phosphate group, chemically classified as a hydrated ammonium magnesium hydrogen phosphate. It occurs as very small, lath-like or platy crystals, which rarely reach macroscopic sizes. Crystals are typically colorless to white and transparent. They often form radial or divergent aggregates. A characteristic feature is a strong, pearly luster on surfaces of perfect cleavage. ## Physical Properties This mineral is very soft and brittle. Its density is approximately 1.73 g/cm³. It exhibits transparency and a white streak. The luster on fracture surfaces is vitreous, while on cleavage planes it is distinctly pearly. Due to its chemical composition and hydration, it is unstable under variable humidity and temperature conditions. ## Colors and Varieties Schertelite is usually colorless or white. No colored varieties or commercial names are distinguished for it. ## History and Name The mineral was first described in 1917 by Samuel George Gordon and J. E. Whitfield. The name was given in honor of Aristides Schertel (1856-1929), a professor of chemistry at the Freiberg Mining Academy in Germany, for his contributions to chemical mineralogy. ## Applications Schertelite has no industrial applications. Its significance is purely scientific and as a collector's item, as a rare product of processes occurring in guano deposits.

Properties

Luster
Peary
Streak
White
Density
1.735
Cleavage
Perfect on {010}
Transparency
Transparent
Crystal system
Orthorhombic

Diagnostic features

## Identification A key diagnostic feature of schertelite is its specific occurrence environment – caves with bat guano deposits. Visually, it can be recognized by small, lath-like crystals with a strong pearly luster on cleavage planes. It is very soft and light. However, final confirmation of its identity requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical analysis. ## Distinguishing from Similar Minerals Schertelite can be confused with other rare phosphates found in guano, such as struvite, hannayite, or newberyite. Struvite often forms larger, better-formed crystals. Hannayite crystallizes in the triclinic system and has different optical properties. Without laboratory access, distinguishing these minerals based on appearance is practically impossible. ## Crystal Forms Schertelite forms thin, flattened crystals with a lath-like or platy habit. They usually occur as small, radial or fan-shaped aggregates and crusts on the surface of rocks or other material in caves.

Geological environment

## Genesis Schertelite is a secondary mineral, formed under specific conditions in caves with accumulated bat guano. It forms as a result of reactions between solutions rich in ammonia and phosphates, originating from the decomposition of guano, and magnesium ions present in waters percolating through carbonate rocks or other minerals. ## Mineral Associations This mineral co-occurs with other phosphates typical of guano deposits, such as struvite, hannayite, newberyite, dittmarite, monetite, and brushite. ## Localities The most important and historical locality (type locality) is Descubridora Cave on Mona Island, Puerto Rico. It is also known from several other guano caves worldwide, including Arnhem Cave in Namibia and caves in the vicinity of Skipton, Victoria, Australia.

Rarity

Very rare

For collectors

## Quality Criteria The quality of schertelite specimens, being a typical micromineral, is assessed based on the sharpness and development of crystals, even if they are microscopic in size. The most valued are rich aggregates of well-defined, radial clusters on a small rock matrix. The value of a specimen is also enhanced by co-occurrence with other rare minerals from the same paragenesis. ## Popular Localities Specimens of historical significance come from the type locality on Mona Island. Among collectors, more accessible, though still very rare, are specimens from Arnhem Cave in Namibia, which have appeared on the mineral market in recent decades.

Care and storage

## Cleaning Schertelite specimens should only be dry-cleaned, using a very soft brush or a gentle stream of compressed air to remove dust. The mineral is sensitive to water and can be damaged or dissolved upon contact with it. ## What to Avoid Contact with water, detergents, and all chemicals must be strictly avoided. Schertelite is a hydrated mineral, therefore it is sensitive to high temperatures, which can cause dehydration and destruction. It should be protected from direct sunlight and high humidity. It is very brittle, so it requires careful handling. ## Storage It is recommended to store specimens in sealed, airtight containers (e.g., "micromount" type) to protect them from humidity changes, dust, and mechanical damage. It is best kept under stable temperature conditions, away from heat sources and light.

Sources

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