Macivorite

Chemical formula: (N³⁻H₄)₃Al₅(PO₃OH)₆(PO₄)₂(H₂O)₁₂·6H₂O

Macivoryite is an extremely rare aluminum phosphate that forms microscopic, colorless crystals in caves with bat guano.

## Characteristics Macivoryite is a hydrated aluminum ammonium phosphate, occurring as extremely small, colorless, hexagonal or trigonal plates and tabular crystals. Crystals rarely exceed 20 micrometers, making them visible only under high magnification. They typically form scattered aggregates or thin coatings on other minerals. ## Physical properties Due to the microscopic size of the crystals, most physical properties, such as hardness, density, or luster, have not been precisely determined. The crystals are transparent and colorless. ## History and name The mineral was approved by the IMA in 2008. Its name honors Ian Macivor, an Australian mineral collector who discovered the first samples in the Skipton Caves in Australia. It was described by mineralogists D. E. Hibbs, P. Leverett, A. R. Williams, and P. A. Williams. ## Uses Macivoryite has no commercial or industrial applications. Its significance is purely scientific and collectible, as a unique and rare representative of cave minerals.

Properties

Transparency
Transparent
Crystal system
Trigonal

Diagnostic features

## Identification Identification of macivoryite is impossible without advanced laboratory techniques, such as scanning electron microscopy (SEM) combined with EDS analysis or X-ray diffraction (XRD). Under collecting conditions, identification relies solely on a label from a reliable source confirming the analysis. ## Differentiation from similar minerals It can be confused with other microscopic secondary phosphate minerals that form in guano caves, such as tinticite, wardite, or newberyite. Visual differentiation is impossible and requires specialized chemical and structural analysis. ## Crystal forms Macivoryite forms very small, hexagonal or trigonal, tabular crystals, often grouped into rosette aggregates or scattered coatings.

Geological environment

## Genesis Macivoryite is a secondary mineral, forming in the specific environment of caves. Its genesis is related to the reaction of phosphate-rich solutions, derived from the decomposition of bat guano, with aluminum present in the surrounding cave rocks (e.g., in clays). It crystallizes under low-temperature conditions. ## Mineral associations At the type locality (Skipton Caves), it co-occurs with tinticite, montgomeryite, wardite, newberyite, apatite, quartz, and clay minerals. ## Localities The only confirmed occurrence of macivoryite in the world is its type locality – Skipton Caves, located near Mount Widderin in Victoria, Australia.

Rarity

Extremely rare

For collectors

## Quality criteria The quality of a specimen depends on the richness and quantity of microcrystals on the rock matrix. The most desirable samples are those where macivoryite forms well-developed aggregates visible under a microscope, preferably in association with other rare phosphates. Due to the microscopic nature of the mineral, the aesthetics of the specimen are secondary compared to its scientific and documentary value. ## Popular localities The only source of specimens is the Skipton Caves in Australia. Material from this locality is extremely difficult to obtain and appears on the collector's market sporadically.

Care and storage

## Cleaning Macivoryite specimens should not be cleaned mechanically or chemically. Any attempt at cleaning risks irreversible destruction of the microscopic crystals. The specimen should only be protected from dust. ## What to avoid The mineral is likely sensitive to changes in humidity and temperature. Contact with water, chemicals, as well as exposure to direct sunlight and heat sources, should be strictly avoided. Due to its genesis, it may be unstable in a dry environment. ## Storage Specimens should be stored in stable conditions, preferably in a sealed, closed "micromount" box, to protect them from dust, mechanical damage, and humidity fluctuations.

External references

Sources

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