Oftedalite

Chemical formula: K(ScCa)&#₉₇₄₄;₂Be₃Si₁₂O₃₀

Oftedalite is a very rare, purplish mineral from the beryl group, closely related to scandium and milarite.

## Characteristics Oftedalite is an extremely rare mineral belonging to the milarite group. It occurs as small, hexagonal crystals, usually not exceeding 1 mm in diameter. The crystals are prismatic, terminated by flat faces. Its most characteristic feature is its purplish color, although it can also be colorless. ## Physical Properties Oftedalite crystals exhibit a vitreous luster. The mineral is brittle and has an uneven fracture. Its Mohs hardness is approximately 6, and its density is close to 2.75 g/cm³. ## Colors and Varieties Oftedalite occurs in shades from pale violet to purplish, and can also be colorless. No named varieties of this mineral have been distinguished due to its extreme rarity. ## History and Name The mineral was named in honor of Ivar Werner Oftedal (1894-1975), a Norwegian mineralogist and geochemist from the University of Oslo, who was the first to study scandium-rich minerals from Norwegian pegmatites. It was officially recognized by the IMA in 2003. The type locality (locus typicus) is the Tørdal granite quarry in the Telemark region, Norway. ## Uses Oftedalite has no industrial application. Its significance is purely scientific and as a collector's item, and due to its rarity and small crystal size, it is a coveted object for specialized collectors of rare minerals.

Properties

Mohs hardness: 6
Luster: Vitreous
Streak: White
Density: 2.75
Cleavage: None
Fracture: Uneven
Transparency: Transparent to translucent
Crystal system: Hexagonal

Diagnostic features

## Identification Identifying oftodalite without advanced analytical methods (such as EDS/WDS) is practically impossible. Preliminary identification is based on the hexagonal crystal form, purplish color, vitreous luster, and occurrence in a specific geological environment - scandium-rich granitic pegmatites. The origin locality (Tørdal, Norway) is a crucial clue. ## Distinguishing from Similar Minerals Oftedalite is visually almost identical to other minerals of the milarite group, such as milarite itself, berezanskite, or sogdianite. Definitive distinction requires chemical analysis to confirm the dominance of scandium in a specific structural position. Other purple minerals of similar form, such as sugilite, can also be misleading, but they occur in different parageneses. ## Crystal Forms It forms short, prismatic crystals with a hexagonal cross-section, terminated by a pinacoid. Crystals are usually very small, rarely exceeding 1 mm in length and width.

Geological environment

## Genesis Oftedalite crystallizes in the late stage of granitic pegmatite evolution, under conditions enriched in rare earth elements, including scandium, as well as beryllium and potassium. It forms in miarolitic cavities and rock voids in amazonite-type pegmatites. ## Mineral Associations This mineral occurs in association with other pegmatitic minerals, such as quartz (smoky variety), microcline (including amazonite), albite, beryl, bazzite, scandiobabingtonite, kaskandyte, and milarite. ## Localities The only confirmed occurrence of oftodalite in the world is its type locality: the Tørdal granite quarry, in the municipality of Drangedal, Telemark region in southern Norway.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of an oftodalite specimen is primarily determined by the size and quality of the crystals. The most prized specimens are those with well-formed, sharp crystals of intense purple color, contrastingly set on a matrix of quartz or feldspar. Due to the microscopic nature of the mineral, even a small but well-defined crystal is considered valuable. The presence of associated minerals, such as bazzite, enhances the attractiveness of the specimen. ## Popular Localities The only source of oftodalite is the Tørdal quarry in Norway. All specimens available on the collector's market originate from this single locality.

Care and storage

## Cleaning Due to its extreme rarity and fragility, oftodalite specimens, if they require cleaning at all, should be handled with the utmost care. Only gentle dust removal with a soft brush or a photographic blower is recommended. Contact with water and any chemicals should be avoided. ## What to Avoid Avoid ultrasonic cleaners, chemical agents, sudden temperature changes, and direct sunlight. The mineral is brittle, so it should be protected from impacts and scratches. ## Storage Oftedalite specimens, typically microscopic and embedded in matrix rock, should be stored in specialized perky boxes that protect against dust and mechanical damage. Avoid storage in humid environments.

Sources

IMA Mineral List (CNMNC)