Holtedahlite

Chemical formula: Mg₁₂(PO₃OH,CO₃)(PO₄)₅(OH,O)₆

Holtedahlite is a rare, light blue or colorless phosphate mineral, found in igneous rocks and skarns in Norway.

## Characteristics Holtedahlite is a complex magnesium phosphate that typically forms granular or massive aggregates within the host rock. It rarely occurs as well-formed crystals, and if so, they are small and have a hexagonal outline. Most often, it is observed as inclusions in other minerals, with a light blue, bluish-green, or colorless hue. ## Physical Properties This mineral is characterized by a hardness of approximately 6 on the Mohs scale. It has a vitreous luster and is usually translucent. Its density is close to 3.15 g/cm³. ## Colors and Varieties Holtedahlite occurs in shades ranging from light blue and bluish-green to colorless. No named varieties have been distinguished. ## History and Name The mineral's name honors Olaf Holtedahl (1885–1975), a Norwegian geologist and professor at the University of Oslo. Holtedahlite was first described in 1957 based on material found in the Tingelstadtjern igneous complex in Modum, Norway. ## Uses Due to its rarity and typically small size, holtedahlite has no industrial application and is solely an object of interest for collectors specializing in rare minerals and scientists.

Properties

Mohs hardness
4.5-5
Color
Colorless
Luster
Vitreous
Streak
White
Density
2.94
Cleavage
Shows no cleavage
Fracture
Irregular/Uneven
Transparency
Transparent
Crystal system
Trigonal

Diagnostic features

## Identification Field identification of holtedahlite is very difficult. It requires specialized laboratory tests, such as chemical analysis (EDS) and X-ray diffraction (XRD). In a collection, it can be preliminarily recognized by its light blue color, vitreous luster, and co-occurrence with characteristic minerals from its type locality. ## Distinguishing from Similar Minerals It can be confused with other blue or colorless phosphate or silicate minerals found in similar environments, such as apatite or certain amphiboles. Definitive differentiation is only possible using advanced analytical methods. ## Crystal Forms Holtedahlite crystallizes in the hexagonal system. It most often forms anhedral (unformed) grains and massive aggregates. Small, hexagonal prismatic crystals are rarely found.

Geological environment

## Genesis Holtedahlite is a mineral of magmatic or metamorphic origin. It forms in serpentinites metamorphosed under amphibolite facies conditions, as well as in magnesian skarns. In its type locality (Tingelstadtjern), it occurs in an albite-plagioclase dike cutting serpentinites. ## Mineral Associations This mineral co-occurs with minerals such as albite, magnesite, sapphirine, phlogopite, enstatite, cordierite, clinochlore, apatite, talc, and spinel. ## Localities The most important and best-documented occurrences of holtedahlite are in Norway. Besides the type locality in Tingelstadtjern (Modum), it has also been found in magnesian skarns in the Kitteln and Gruva mines in the Nordland region.

Rarity

Very rare

For collectors

## Quality Criteria The most sought-after specimens by collectors are those with visible, even if small, aggregates of holtedahlite with an intense blue color, contrasting with the light host rock. Due to the rarity of well-formed crystals, even granular aggregates rich in the mineral are considered valuable. ## Popular Localities By far the most prized specimens come from Norway, especially from the type locality in Tingelstadtjern, Modum. Material from mines in the Nordland region is also sought after by specialized collectors.

Care and storage

## Cleaning It is recommended to clean specimens only with a soft, dry brush to remove dust. The use of water, especially with detergents, is inadvisable due to the mineral's possible reactivity. ## What to Avoid Avoid contact with acids and other chemicals that may damage the mineral's surface. It should not be heated or subjected to ultrasound. Prolonged exposure to strong sunlight may not be harmful, but caution is advised. ## Storage Holtedahlite specimens, often occurring as inclusions in rock, are best stored under stable conditions in a closed display box to protect them from dust and mechanical damage.

External references

Sources

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