Ferrolaueite

Chemical formula: Fe<sup>2+</sup>Fe<sup>3+</sup><sub>2</sub>(PO<sub>4</sub>)<sub>2</sub>(OH)<sub>2</sub>·8H<sub>2</sub>O

Ferrolaueite is a rare, hydrated iron phosphate, forming small, platy crystals of a honey-yellow to reddish-brown color.

## Characteristics Ferrolaueite is a rare phosphate mineral belonging to the laueite group, chemically classified as a hydrated ferrous-ferric iron phosphate. It occurs as small, platy or short-prismatic crystals, which often form rosette-like or radial aggregates. Its crystals are typically very small, rarely exceeding a millimeter in size. ## Physical Properties This mineral is characterized by a hardness of 3 on the Mohs scale. It has a vitreous luster and is transparent to translucent. The density of ferrolaueite is approximately 2.56 g/cm³. ## Colors and Varieties Ferrolaueite most commonly exhibits honey-yellow, orange-yellow, reddish-brown, or brown colors. No distinct varieties are recognized. ## History and Name The name "ferrolaueite" refers to its chemical composition – the dominance of iron (Latin: *ferrum*) – and its structural and chemical similarity to laueite. It was first described in 1988 based on material from the Palermo No. 1 mine in New Hampshire, USA, although it was identified as a distinct mineral as early as 1954.

Properties

Mohs hardness
3
Luster
Vitreous
Streak
Pale yellow
Density
2.56
Cleavage
Good on {010}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Triclinic

Diagnostic features

## Identification Ferrolaueite is identified by its characteristic honey-yellow to reddish-brown color, platy crystal habit, often forming rosette aggregates, and its occurrence in granitic pegmatites. Low hardness (3) and vitreous luster are also important diagnostic features. ## Distinguishing from Similar Minerals It can be confused with other secondary phosphate minerals such as laueite, stewartite, or strunzite. Laueite has a very similar appearance but usually a lighter, yellow color. Stewartite forms fibrous aggregates, not platy crystals. Accurate differentiation of these minerals often requires chemical (EDS) or X-ray (XRD) analysis. ## Crystal Forms It forms thin to thick platy crystals, flattened parallel to {010}, with an approximately square or octagonal cross-section. Crystals often occur as radial or rosette aggregates.

Geological environment

## Genesis Ferrolaueite is a secondary phosphate mineral that forms as a result of hydrothermal alteration or weathering of primary phosphates (mainly triphylite) in complex granitic pegmatites. It forms in oxidation zones under low-temperature conditions. ## Mineral Associations It often co-occurs with other secondary phosphates such as rockbridgeite, strunzite, stewartite, laueite, strengite, as well as quartz, muscovite, and goethite. The primary mineral from which it forms is typically triphylite. ## Localities The most important and classic localities for this mineral are pegmatites in the USA, particularly the Palermo No. 1 mine in North Groton, New Hampshire (type locality) and the Tip Top mine in Custer County, South Dakota. It is also known from several occurrences in Germany (e.g., Hagendorf-Süd, Bavaria) and Portugal.

Rarity

Rare

For collectors

## Quality Criteria The most prized specimens by collectors are those with well-formed, sharp crystals of intense honey-yellow or orange color, forming aesthetic, rosette-like aggregates. Contrast with a light matrix, such as quartz, significantly enhances the specimen's appeal. Due to the small size of the crystals, their quality and perfect formation visible under magnification are crucial. ## Popular Localities Specimens from the type locality, the Palermo No. 1 mine in New Hampshire, and from the Tip Top mine in South Dakota, USA, are considered classic and most sought after by specialists collecting rare phosphates.

Care and storage

## Cleaning Due to its low hardness and potential fragility, specimens should be cleaned very carefully. The safest method is to use compressed air to remove dust. If wet cleaning is necessary, use only distilled water and a soft brush, then quickly and thoroughly dry the specimen, avoiding elevated temperatures. ## What to Avoid Avoid ultrasonic cleaners, chemical agents, acids, and detergents. As a hydrated mineral, ferrolaueite is sensitive to heat, which can lead to dehydration and destruction of the crystals. It should be protected from prolonged exposure to direct sunlight and moisture. ## Storage Ferrolaueite specimens, due to their small size and fragility, are best stored in small, sealable "micromount" boxes lined with soft material. This protects them from mechanical damage and dust.

Sources

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