Friisite

Chemical formula: Pb<sub>8</sub>Al<sub>3</sub>Si<sub>8</sub>O<sub>27</sub>Cl<sub>3</sub>

Friisite is an extremely rare lead, aluminum, and silicon mineral, discovered in the Ilímaussaq complex in Greenland, distinguished by its unique chemical composition.

## Characteristics Friisite is a silicate mineral characterized by a very complex chemical composition containing lead, aluminum, silicon, oxygen, and chlorine. It occurs as extremely small, anhedral (lacking crystal faces) grains, usually not exceeding 50 micrometers in size. These grains are most often intergrown with other minerals, mainly ussingite. Due to its microscopic size, its visual features cannot be assessed with the naked eye. ## Physical Properties Due to its extreme rarity and microscopic grain size, most of friisite's physical properties have not been determined. Hardness, density, cleavage, and fracture remain unknown. Its luster is described as vitreous. The mineral is transparent to translucent. ## Colors and Varieties Friisite is colorless. No colored varieties or commercial forms are known. ## History and Name The mineral was approved by the International Mineralogical Association (IMA) in 2023 under number IMA2023-085. The name honors Henrik Friis, a Danish mineralogist and curator of collections at the Natural History Museum of Denmark, for his contributions to the study of the mineralogy of the Ilímaussaq complex. It was discovered in material from a historical sample collected in 1978 in the Kvanefjeld mine in Greenland. ## Uses Friisite has no practical or commercial applications. Its significance is purely scientific and as a collector's item, as a unique and newly discovered mineral species.

Properties

Luster
Vitreous
Transparency
Transparent to translucent
Crystal system
Trigonal

Diagnostic features

## Identification Identification of friisite is impossible without advanced analytical techniques. Due to its microscopic size and occurrence as inclusions, identification relies solely on methods such as electron microprobe (EDS/WDS) to determine chemical composition and electron diffraction to establish crystal structure. ## Distinguishing from Similar Minerals Visually, as a colorless, microscopic grain, it is indistinguishable from many other minerals found in similar environments. Only laboratory analyses provide certainty of identification. ## Crystal Forms Friisite forms exclusively anhedral, irregular grains up to 50 µm in size, intergrown with other minerals, mainly ussingite.

Geological environment

## Genesis Friisite forms under hydrothermal conditions within highly alkaline, nepheline syenites and their pegmatites. It is a late-stage crystallization mineral, forming in ussingite veins cutting through host rocks such as lujavrite. ## Mineral Associations This mineral occurs in close association with ussingite (as inclusions), and also with analcime, natrolite, aegirine, arfvedsonite, microcline, lorenzenite, eudialyte, vitusite-(Ce), and steenstrupine-(Ce). ## Localities The only confirmed occurrence of friisite in the world is its type locality: ussingite veins within the Kvanefjeld tunnel, in the alkaline Ilímaussaq intrusive complex, in the Kujalleq region of southern Greenland.

Rarity

Extremely rare

For collectors

## Quality Criteria As a micromineral of purely scientific importance, standard quality criteria do not apply. The value of a specimen lies in the confirmed presence of friisite within the rock matrix, usually in ussingite. The most valuable specimens are those from the type locality, with the richest mineral associations, whose identity has been analytically confirmed. ## Popular Localities The only source of specimens is the Ilímaussaq complex in Greenland. The material for research comes from historical collections, and obtaining new specimens is extremely difficult.

Care and storage

## Cleaning Specimens containing friisite (typically as microscopic inclusions in ussingite) should be cleaned with the utmost care. Only gentle dust removal with a soft brush or compressed air from a safe distance is recommended. Avoid contact with water and any chemical agents. ## What to Avoid Ultrasonic cleaners, chemical agents, acids, and sudden temperature changes should be absolutely avoided. Coexisting minerals, such as ussingite, may be sensitive to moisture and chemicals. Protect the specimen from direct sunlight, which can affect associated minerals. ## Storage Specimens containing friisite should be stored in stable conditions, in a dry place, away from light sources and contaminants. It is best to place them in a closed display box or cabinet to minimize dust accumulation and the risk of mechanical damage.

Sources

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