Doyleite

Chemical formula: Al(OH)<sub>3</sub>

Doyleite is a rare polymorph of aluminum hydroxide, occurring as small, colorless or white, tabular crystals.

## Characteristics Doyleite is one of four polymorphic varieties of aluminum hydroxide, Al(OH)₃, which also include gibbsite, bayerite, and nordstrandite. This mineral forms very small, most often microscopic, tabular crystals with a hexagonal outline. It usually occurs in rosette-like or spherulitic aggregates, as well as coatings and efflorescences. It is colorless to white, rarely with a creamy or yellowish tint. Due to the small size of the crystals, its macroscopic features are difficult to observe. ## Physical Properties Doyleite has a hardness in the range of 2.5-3 on the Mohs scale. It exhibits perfect cleavage in one direction, parallel to the crystal base. The luster is vitreous, and on cleavage planes, it can be pearly. It is a light mineral, with a density of approximately 2.52 g/cm³. ## Colors and Varieties The mineral is typically colorless or white. No colored or commercial varieties are distinguished. ## History and Name The mineral is named in honor of Earl J. Doyle (1905-1991), a Canadian mineral collector who first found this mineral. Doyleite was described and approved as a new mineral species in 1980 by George Y. Chao, D.C. Harris, A.C. Roberts, A.P. Sabina, and A.J. Perrault. The type locality is the Francon Quarry in Montreal, Canada. ## Applications Due to its rarity and microscopic size, doyleite has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals and micromounts.

Properties

Mohs hardness
2.5-3
Luster
Vitreous, Pearly
Streak
White
Density
2.52
Cleavage
Perfect on {001}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Triclinic

Diagnostic features

## Identification Identification of doyleite based on visual characteristics is practically impossible due to the microscopic size of the crystals. Definitive identification requires advanced analytical methods, such as X-ray diffraction (XRD) or Raman spectroscopy, which allow it to be distinguished from other Al(OH)₃ polymorphs. ## Distinguishing from Similar Minerals Doyleite is most often confused with other aluminum hydroxide polymorphs: gibbsite, bayerite, and nordstrandite. All have identical chemical compositions and similar appearances. Gibbsite and nordstrandite crystallize in the monoclinic system, while doyleite crystallizes in the triclinic system, which is a key distinguishing feature, ascertainable only by laboratory methods. It can also be confused with microcrystalline calcite or other carbonates, from which it is distinguished by its lack of reaction with hydrochloric acid. ## Crystal Forms Doyleite forms thin, tabular crystals with a hexagonal outline. These crystals often combine into rosette-like or fan-shaped aggregates. It also occurs as spherulitic clusters and thin coatings on other minerals.

Geological environment

## Genesis Doyleite is a low-temperature mineral, forming under hydrothermal conditions. It forms in voids and fissures in various rock types. At its type locality (Francon Quarry in Canada), it occurs in a syenite dike cutting limestones. It is also found in weathering zones of aluminum-rich rocks and in cave deposits (speleothems). ## Mineral Associations This mineral is often accompanied by other Al(OH)₃ polymorphs (gibbsite, nordstrandite, bayerite). Depending on the location, it co-occurs with minerals such as: weloganite, dresserite, hydrodresserite (Francon Quarry, Canada); cryolite, chiolite, ralstonite (Ivittuut, Greenland); allophane, gibbsite, quartz (Russia). ## Localities The most important and best-documented doyleite localities worldwide include: - Canada: Francon Quarry, Montreal, Quebec (type locality). - Greenland: former cryolite mine in Ivittuut. - Russia: Angren brown coal deposit, Uzbekistan; Festivalnoye tin and polymetallic deposit in Siberia. - United States: Lechuguilla Cave in New Mexico. - Hungary: bauxite mine in Gánt, Fejér County.

Rarity

Very rare

For collectors

## Quality Criteria For doyleite, a typically microscopic mineral, the main criterion for collector value is the overall quality and richness of the specimen. Most prized are samples with well-formed, sharp microcrystals forming aesthetic, rosette-like aggregates. Contrast with the rock matrix and the presence of rare associated minerals, especially from the type locality (Francon), are also important. The size of individual crystals rarely exceeds fractions of a millimeter, so any specimen with visible clusters to the naked eye is considered exceptional. ## Popular Localities Specimens from the type locality – the now-closed Francon Quarry in Montreal, Canada – are by far the most sought after by collectors. This locality is famous for the occurrence of many rare minerals, and doyleite in association with weloganite or dresserite is a classic for micromount collectors.

Care and storage

## Cleaning Doyleite specimens should be cleaned with the utmost care, preferably using compressed air to remove dust. Due to its low hardness and perfect cleavage, mechanical cleaning, including brushing, should be avoided. If liquid is necessary, brief rinsing in distilled water is recommended, followed by thorough drying. ## What to Avoid Doyleite is sensitive to acids and bases, which can chemically etch it. Contact with all household and laboratory chemicals should be avoided. The mineral is brittle and soft, so it must be protected from impacts, scratching, and vibrations. It should not be heated. ## Storage The safest method for storing doyleite specimens, especially micromounts, is in sealed plastic boxes (e.g., "membrane boxes" or boxes with foam inserts), which protect against dust and mechanical damage. Exposure to humid environments should be avoided.

External references

Sources

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