Nannoniite

nannoniite

gibbsite

weloganite

dawsonite

Images

Formula: Al2(OH)5F
Hydroxide, epitaxial on weloganite
Crystal system: Monoclinic
Specific gravity: 2.492 calculated (Mindat)
2.43 measured and 2.51 calculated for material from the Francon Quarry (AM 110.5.829)
Hardness: 2 to 3
Streak: White
Colour: Colourless to white
Luminescence: Bluish-white fluorescence under short wave UV (λ=254 nm) and a yellowish-white fluorescence under long wave UV (λ=350 nm). Also phosphorescent (material from the Francon quarry)
Environments

Sedimentary environments
Hydrothermal environments

Nannoniite has been known as an unnamed gibbsite-like mineral since 1968, and it was not until 2024 that it was approved as a new mineral with the name "nannoniite".

Localities

At the Francon quarry, Montréal, Québec, Canada, in 1979 a gibbsite-like mineral that was finally identified, in 2024, as nannoniite was found. It was described as chalk-white powdery coatings, porcelain-like and waxy granular material, white translucent globules and botryoidal crusts and white shells. The globules are typically 0.1 to 0.2 mm across and consist of radial aggregates. Some glob ules have coalesced into botryoidal crusts; surface areas of the crusts are generally no more than 1 to 2 mm2, and contamination by dawsonite, fluorite, calcite and halloysite is common (CM 28.1.147-153).
Nannoniite is extremely widespread at the Francon Quarry and is present on or associated with most samples of weloganite (AM 110.5.829).
Nannoniite from the Francon Quarry - Image

At the type locality, Le Cetine di Cotorniano Mine, Chiusdino, Siena Province, Tuscany, Italy, the unnamed mineral first reported from the Francon Quarry in Canada and formerly known as “UM1990-28:OHF:Al” has been approved under the name nannoniite. This mineral was first reported in 1968 in the type description of weloganite as an unidentified mineral that yielded a powder X-ray diffraction pattern similar to that of gibbsite. Although nannoniite is presently (May 2025) known from just four localities, it is relatively common at two of them, the Francon quarry and Le Cetine di Cotorniano Mine; it is widespread in cavities within silicified limestone at the Italian type locality (AM110.5.829).
Nannoniite occurs as (hemi-)spherical aggregates, up to 1 mm in diameter, formed by spindle-like crystals or tabular individuals. Associated minerals include alunite, baryte, gypsum and quartz (Mindat).

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