Thortveitite

Chemical formula: Sc₂Si₂O₇

Thortveitite is a very rare scandium silicate, prized by collectors as one of the primary sources of this element.

## Characteristics Thortveitite is an extremely rare mineral from the sorosilicate group, consisting mainly of scandium silicate. In its pure form, it is colorless or gray, but the most commonly found specimens range in color from grayish-green, through yellowish, to black, which is a result of impurities. It forms elongated, prismatic crystals, often with longitudinal striations on the faces. It usually occurs as single crystals or radial aggregates, embedded in the host rock, which is most often granitic pegmatites. ## Physical Properties This mineral is characterized by significant hardness, ranging from 6-7 on the Mohs scale, making it resistant to scratches. It has a vitreous or almost adamantine luster. It is a relatively dense mineral, with a density of about 3.57 g/cm³. It is usually translucent, and in thin fragments, it can be transparent. ## Colors and Varieties The dominant color of thortveitite is grayish-green to black. Rarer specimens are gray, yellowish, and even bluish. The color variation is mainly due to the presence of impurities of other elements, such as iron, yttrium, or lanthanides, which substitute for scandium in the crystal structure. No named commercial or color varieties are distinguished. ## History and Name The mineral is named in honor of the Norwegian engineer and mineral collector, Oskar Thortveit (1872–1917), who first found its specimens. The mineral was described and named in 1911 by the Norwegian geologist and mineralogist Johan Herman Lie Vogt. ## Uses Thortveitite, due to its high scandium content (up to 40% scandium oxide), was historically one of the first and most important sources of this element. Scandium is used in advanced aluminum alloys (e.g., in the aerospace industry), in high-intensity lighting, and in lasers. From a collector's perspective, thortveitite is valued for its rarity and as a classic example of scandium mineralogy.

Properties

Mohs hardness: 6-7
Color: Greyish-green, black, grey, blue, yellow, brown
Luster: Vitreous
Streak: White
Density: 3.27
Cleavage: Imperfect on {110}
Fracture: Irregular/Uneven,Conchoidal
Transparency: Translucent,Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Thortveitite can be identified by its characteristic, elongated prismatic crystals, often with longitudinal striations. Its high hardness (6-7) and relatively high density are helpful features. The color, most often in shades of grayish-green to black, combined with a vitreous luster, is also diagnostic. Its occurrence in granitic pegmatites is a key field indicator. ## Distinguishing from Similar Minerals Thortveitite is sometimes confused with other dark prismatic minerals found in pegmatites, such as tourmaline (schorl), epidote, or pyroxenes (e.g., augite). It is distinguished from tourmaline by the absence of the characteristic triangular crystal cross-section. Epidote usually has a more intense, pistachio-green color and perfect cleavage in one direction, which thortveitite lacks. Pyroxenes typically have cleavage at an angle close to 90 degrees, which differentiates them from thortveitite. ## Crystal Forms Thortveitite crystals are usually columnar or prismatic, elongated along one axis. They often exhibit vertical striations on the prism faces. They occur as single crystals embedded in rock or form fan-shaped and radial aggregates.

Geological environment

## Genesis Thortveitite is a magmatic mineral, crystallizing in the late stages from residual melts rich in rare elements. It forms almost exclusively in granitic pegmatites, where elements that do not fit into the structures of common rock-forming minerals, such as scandium, are concentrated. ## Mineral Associations This mineral co-occurs with other minerals typical of granitic pegmatites, especially those containing rare earth elements. Its most common associations include: albite, microcline, quartz, biotite, muscovite, as well as rarer minerals such as beryl, monazite, xenotime, fergusonite, gadolinite, and euxenite. ## Localities The most important and historical localities for thortveitite are in Norway, particularly in the Iveland and Evje regions, where it was discovered. Significant specimens also come from pegmatites in Madagascar (e.g., in the Befanamo region). Other confirmed localities include Japan, Russia (Urals), and the United States, but specimens from these places are usually much smaller and rarer.

Rarity

Very rare

For collectors

## Quality Criteria The most prized thortveitite specimens are those with well-formed, sharp, and undamaged crystals of significant size. Specimens with a distinct, vitreous luster and partial transparency are also highly valued. Color is less important, although rarer hues, such as bluish, can increase value. Aesthetic composition with a contrasting host rock, such as white albite, is also important. ## Popular Localities Classic and most sought-after specimens by collectors come from the type locality in Norway (Iveland, Evje). Specimens from Madagascar are also highly valued and often reach larger sizes, making them attractive to advanced collectors of systematic minerals and those specializing in pegmatites.

Care and storage

## Cleaning Thortveitite specimens should be cleaned very carefully. It is best to use a soft, dry brush to remove dust. For heavier soiling, distilled water and a delicate brush can be used. Ultrasonic cleaners should be avoided, as they can damage crystals, especially those with internal fractures. ## What to Avoid The mineral is sensitive to strong acids, which can damage it. Sudden temperature changes should be avoided, as they can cause cracks within the crystals. Although relatively hard, it should be protected from impacts and contact with harder minerals (e.g., corundum, diamond) to prevent scratches. ## Storage Thortveitite specimens are best stored in separate, padded collector boxes to prevent abrasions and mechanical damage. Exposure to direct sunlight is not considered harmful, but it is recommended to store them in stable room conditions, away from sources of moisture and chemical contaminants.