Jarlite

Chemical formula: Na₂(Sr,Na)₁₄(Mg,&#₉₇₄₄;)₂Al₁₂F₆₄(OH)₄_

Jarlite is a rare sodium and strontium fluoride, most often forming white, radial aggregates in cryolite pegmatites.

## Characteristics Jarlite is a complex fluoride of sodium, strontium, magnesium, and aluminum, belonging to a group of rare minerals. It most often occurs as aggregates of small, platy or acicular crystals that form characteristic radial, spherulitic, or fibrous aggregates. Less commonly, it is found in granular or massive forms. Well-formed, single crystals are extremely rare and small in size. ## Physical Properties This mineral is characterized by a hardness of 4-4.5 on the Mohs scale, making it relatively soft. Its luster is variable, from vitreous to slightly greasy on fresh surfaces. It is translucent to opaque. The density of jarlite is quite high for a light-colored mineral, ranging from 3.78 to 3.93 g/cm³. ## Colors and Varieties Jarlite is usually white, grayish, or colorless. It can also take on yellowish or pale pink hues. There are no named color varieties or commercial varieties. ## History and Name The mineral was first described in 1933 by the Danish mineralogist Ove Balthasar Bøggild. The name "jarlite" was given in honor of Carl Frederik Jarl (1872–1951), a Danish industrialist and director of Øresunds Chemiske Fabriker, which managed the historic cryolite mine in Ivittuut, Greenland – the mineral's type locality. ## Applications Due to its rarity, jarlite has no industrial applications. It is solely an object of interest for collectors and scientists studying unique mineral parageneses.

Properties

Mohs hardness: 4-4.5
Luster: Vitreous to Greasy
Streak: White
Density: 3.78-3.93
Cleavage: Good on {001} and {110}
Fracture: Uneven
Transparency: Translucent to Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Jarlite is most easily recognized by its characteristic mode of occurrence – white, radial or spherical aggregates. A key diagnostic feature is its geological environment, i.e., its co-occurrence with cryolite and other rare fluorides in pegmatites. Its relatively high density combined with low hardness is also helpful in identification. ## Differentiation from Similar Minerals Jarlite can be confused with other white minerals from the cryolite paragenesis, such as thomsenolite, pachnolite, or gearksutite. These minerals often form similar aggregates. Differentiating them based on visual characteristics can be impossible and requires density testing (jarlite is usually denser) or advanced analytical methods, such as X-ray diffraction (XRD). ## Crystal Forms Jarlite crystals crystallize in the monoclinic system. They almost always occur in aggregates. The most typical forms are radial-fibrous, spherulitic (spherical), and platy aggregates. Single, well-formed crystals are exceptionally rare and appear as small, flattened tablets.

Geological environment

## Genesis Jarlite is a hydrothermal mineral. It forms in the late stages of crystallization of sodium- and fluorine-rich granitic pegmatites, especially in their unique variety – cryolite pegmatites. It forms in vugs and fractures, replacing earlier crystallized minerals. ## Mineral Associations This mineral occurs in association with other, often rare, fluorides. Its most common associations include: cryolite, chiolite, fluorite, topaz, thomsenolite, pachnolite, ralstonite, and gearksutite. ## Localities The most important and historic locality for jarlite is its type locality – the now-inactive cryolite mine in Ivittuut (formerly Ivigtut), Greenland. It is also known from the Ilímaussaq alkaline complex in Greenland. Additionally, it has been reported from the famous Mont Saint-Hilaire locality in Quebec (Canada) and in the alkaline massifs of the Kola Peninsula in Russia (e.g., the Khibiny Massif).

Rarity

Rare

For collectors

## Quality Criteria The most prized specimens by collectors are those with well-formed, spherical or radial aggregates of a pure, white color. Samples in which jarlite contrasts with a colorful rock matrix or co-occurs with other rare minerals from the cryolite paragenesis, such as thomsenolite or pachnolite, are also highly valued. The size of the aggregates and the absence of mechanical damage significantly increase the specimen's value. ## Popular Localities The historical deposit in Ivittuut, Greenland, is considered classic and provides the best jarlite specimens. Material from this locality is the standard for this mineral. Specimens from Mont Saint-Hilaire in Canada, although usually smaller, are also sought after due to the reputation of this locality.

Care and storage

## Cleaning Jarlite specimens should be cleaned very carefully, using a soft brush and distilled water. Ultrasonic cleaners should be avoided, as they can damage delicate, fibrous aggregates. ## What to Avoid Jarlite is relatively soft (4-4.5 on the Mohs scale), making it susceptible to scratches from harder minerals (e.g., quartz, fluorite). Contact with acids and strong chemicals should be avoided. There is no detailed data on its sensitivity to light or temperature, but it is recommended to avoid prolonged exposure to direct sunlight and extreme thermal changes. ## Storage Collector's specimens of jarlite should be stored in separate, padded boxes to protect them from mechanical damage and scratching. It is best to keep them in stable room conditions, away from dust and moisture.

Sources

IMA Mineral List (CNMNC)