Peisleyite
Chemical formula: Na<sub>3</sub>Al<sub>16</sub>(PO<sub>4</sub>)<sub>10</sub>(S<sup>6+</sup>O<sub>4</sub>)<sub>2</sub>(OH)<sub>17</sub>·20H<sub>2</sub>O
Peisleyite is an extremely rare, hydrated sodium aluminum sulfate phosphate, forming pearly aggregates of tiny, hexagonal plates.
Description
## Characteristics Peisleyite is a secondary mineral, occurring as chalky-white, earthy, or compact aggregates. These are composed of extremely small, hexagonal platy crystals, which can only be seen under high magnification. These aggregates often form rosettes, coatings, or thin veins in the host rock. Its appearance can be inconspicuous and easy to overlook. ## Physical Properties Due to the microscopic size of the crystals and the nature of the aggregates, precise determination of peisleyite's hardness and density is impossible. The mineral is characterized by a pearly luster on the plate surfaces and is translucent. ## Colors and Varieties Peisleyite occurs exclusively in white. No colored varieties or trade names are known. ## History and Name The mineral was discovered in the Iron Monarch quarry in South Australia and described in 1993. Its name honors Vincent Peisley (1923–2011), an Australian mineral collector who found the first specimens of this mineral. ## Applications Peisleyite has no industrial application. Its significance is purely scientific and for collectors, as a unique and rare mineralogical species.
Diagnostic features
## Identification Identifying peisleyite based on visual characteristics is very difficult. Key indicators include its chalky-white color, pearly luster (visible under a microscope), aggregate form (rosettes, coatings), and co-occurrence with other rare phosphates. Definitive identification requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical microanalysis (EDS). ## Distinguishing from Similar Minerals Peisleyite can be easily confused with other white, secondary phosphate minerals of similar appearance, such as leucophosphite, crandallite, wavellite, or clay minerals. Distinguishing it in the field or without specialized equipment is practically impossible. The only clue might be the specific mineral association from the type locality. ## Crystal Forms It forms aggregates composed of microscopic, thin, hexagonal plates. These aggregates take the form of rosettes, spherulites, coatings, and efflorescences.
Geological environment
## Genesis Peisleyite is a secondary mineral, forming in the oxidation zone of iron ore deposits rich in phosphorus. It forms as a result of hydrothermal processes or weathering, through the alteration of earlier phosphate minerals in an environment rich in aluminum and sulfates. ## Mineral Associations This mineral occurs in association with other phosphates, such as leucophosphite, crandallite, strengite, wavellite, turquoise, and variscite. ## Localities The only confirmed locality of peisleyite in the world is its type locality – the Iron Monarch quarry, Iron Knob, on the Eyre Peninsula in South Australia.
Rarity
Extremely rare
Collector aspects
## Quality Criteria As a microscopic mineral, peisleyite is primarily valued by specialized collectors (so-called micromounters). The value of a specimen is determined by the abundance of aggregates on the rock matrix, the degree of development of rosettes, and the presence of well-crystallized associated minerals. Due to its rarity, every authentic specimen is considered valuable. ## Popular Localities All known collector specimens come from a single location in the world: the Iron Monarch quarry in South Australia.
Care and storage
## Cleaning Peisleyite specimens are extremely delicate. Mechanical cleaning and contact with water should be avoided. Only careful dust removal with a photographic air blower or compressed air from a distance is permissible. ## What to Avoid The mineral is sensitive to all chemicals, especially acids. Ultrasonic cleaners, high temperatures, and moisture, which can lead to its degradation, should be avoided. ## Storage It is recommended to store specimens in closed, airtight containers (e.g., micromount type) to protect them from dust, mechanical damage, and changes in ambient humidity.