Høgtuvaite

Chemical formula: Ca<sub>4</sub>(Fe<sup>2+</sup><sub>6</sub>Fe<sup>3+</sup><sub>6</sub>)O<sub>4</sub>[Si<sub>8</sub>Be<sub>2</sub>Al<sub>2</sub>O<sub>36</sub>]

Høgtuvaite is a very rare, black mineral from the gadolinite group, discovered in Norway, distinguished by its complex chemical composition.

## Characteristics Høgtuvaite is a black mineral with a vitreous to resinous luster. It occurs as subhedral (poorly formed) grains, reaching sizes of up to 1-2 mm. It typically forms granular aggregates in association with other minerals. It is opaque and is part of the gadolinite supergroup. ## Physical Properties This mineral is characterized by a Mohs hardness of approximately 6. Its density is relatively high, with a measured value of 3.84 g/cm³. It has a vitreous to resinous luster and a black streak. It exhibits no cleavage, and its fracture is conchoidal. ## Colors and Varieties Only the black variety of this mineral has been described to date. No other color varieties or trade names are known. ## History and Name The mineral's name comes from its discovery locality – the Høgtuva complex in northern Norway. It was approved as a new mineral species by the International Mineralogical Association (IMA) in 1999. It was described by G. Raade, G. Ferraris, G. Gula, G. Ivaldi, and P. J. Utochkin. ## Applications Due to its extreme rarity, høgtuvaite has no industrial applications. It is solely an object of scientific interest and a collector's item for specialized collectors of rare minerals.

Properties

Mohs hardness
6
Luster
Vitreous to Resinous
Streak
Black
Density
3.84
Cleavage
None
Fracture
Conchoidal
Transparency
Opaque
Crystal system
Monoclinic

Diagnostic features

## Identification Identifying høgtuvaite in the field is practically impossible. Identification requires advanced analytical methods, such as X-ray diffraction (XRD) and chemical microanalysis (EDS/WDS), due to its resemblance to other black, heavy minerals. ## Distinguishing from Similar Minerals It can be confused with other minerals from the gadolinite supergroup, such as gadolinite-(Y) or datolite, as well as more common minerals like tourmaline (schorl) or ilmenite. Differentiation is based on precise determination of chemical composition (presence of beryllium, calcium, and iron proportions) and crystallographic data. ## Crystal Forms Høgtuvaite forms poorly developed, subhedral crystals of small size, usually not exceeding 1-2 mm. They occur as individual grains or irregular aggregates within the host rock.

Geological environment

## Genesis Høgtuvaite forms under specific metamorphic conditions. It was found in metasomatically altered amphibolite lenses occurring within gneisses. Its formation is associated with hydrothermal processes and metasomatism in contact zones of different rock types. ## Mineral Associations This mineral co-occurs with a range of other minerals, such as albite, quartz, titanite, cordierite, muscovite, biotite, chlorite, epidote, allanite-(Ce), zircon, apatite, and also with minerals from the gadolinite group. ## Localities The only confirmed occurrence of høgtuvaite in the world is its type locality – the Høgtuva tectonic window complex in the Nordland region of Norway.

Rarity

Extremely rare

For collectors

## Quality Criteria As a mineral of primarily scientific and systematic importance, the main criterion for a collector's value is the certainty of specimen identification, confirmed by analysis. Grain size and abundance within the rock matrix also increase its attractiveness. Specimens with well-visible, though poorly formed, crystals in association with other rare minerals are the most desirable. ## Popular Localities The only source of specimens is the type locality in Norway. Material from this location is extremely difficult to acquire and rarely appears on the collector's market.

Care and storage

## Cleaning Cleaning is recommended only with a soft brush to remove dust. The use of water, especially with detergents, is inadvisable due to a lack of data on its reactivity. ## What to Avoid Avoid contact with chemicals, acids, and bases. The mineral should be protected from extreme temperatures and ultrasonic cleaning, which could damage delicate specimens. Store away from moisture. ## Storage Høgtuvaite specimens, being extremely rare and usually small, are best stored in specialized display boxes or micromounts, protecting them from dust and mechanical damage. Direct exposure to sunlight should be avoided.

Sources

Read more