Wöhlerite

Chemical formula: Na₂Ca₄Zr⁴⁺(Nb⁵⁺,Ti⁴⁺)(Si₂O₇)₂(O,F)₄

A rare zirconium and niobium silicate, forming tabular, vitreous crystals with a honey-yellow or brown color.

## Characteristics Wöhlerite is a complex silicate from the sorosilicate group, containing zirconium, niobium, and calcium. It occurs as tabular or prismatic crystals, often with rich face morphology. It is usually embedded in rock, and well-formed, freestanding crystals are rare. Its appearance is characterized by a vitreous to resinous luster and colors ranging from light yellow, through honey-yellow, to reddish-brown.

Properties

Mohs hardness: 5.5-6
Color: Honey-yellow, wine-yellow to sulfur-yellow, light to dark yellow, brown, gray
Luster: Vitreous to resinous
Streak: Yellowish white; pale yellow
Density: 3.40
Cleavage: Distinct on {010} Poor on {100}{110}
Fracture: Irregular/Uneven,Splintery
Transparency: Transparent,Translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Characteristic features of wöhlerite include its tabular or thick-tabular crystal habit, vitreous to resinous luster, and typical colors (yellow, brown). Perfect cleavage in one direction is a key diagnostic feature, if observable. Occurrence in nepheline syenites is also a strong indicator. ## Distinguishing from Similar Minerals It can be confused with other minerals from the wöhlerite group (such as låvenite or hiortdahlite), from which differentiation without advanced analysis (XRD, EDS) is practically impossible. It can also be mistaken for some zircons, titanite, or epidote. It differs from zircon by its lower hardness and crystal habit. Titanite often has a more wedge-shaped form and stronger luster. Epidote usually occurs in different parageneses and has a greenish color. ## Crystal Forms Wöhlerite crystals are monoclinic and most often take the form of tablets, short prisms, or irregular grains. They often form granular or radial aggregates. Well-formed, single crystals are rare and prized.

Geological environment

## Genesis Wöhlerite is an igneous mineral, typical of alkaline intrusive rocks, especially nepheline syenites and associated pegmatites. It forms in the late stages of crystallization of magma rich in elements such as zirconium, niobium, and sodium, and poor in silica.

Rarity

Rare

For collectors

## Quality Criteria The most valued specimens by collectors are those with sharp, well-formed, single crystals of a distinct honey-yellow color and good transparency. Crystal size is of great importance – those exceeding 1 cm are already considered significant. Attractiveness is enhanced by a contrasting placement on a light rock matrix, for example, on albite or nepheline. ## Popular Localities By far the most sought-after specimens come from classic localities in Norway, in the Langesundsfjorden area. Material from Mont Saint-Hilaire in Canada also provides good quality crystals, often in interesting mineral associations. Specimens from the Kola Peninsula are usually more massive and less frequently form freestanding crystals.

Care and storage

## Cleaning Wöhlerite specimens should be cleaned very carefully, using a soft brush to remove dust. If necessary, distilled water can be used, but prolonged soaking should be avoided. Due to its perfect cleavage, mechanical cleaning (e.g., ultrasonics) is absolutely not recommended, as it can lead to crystal disintegration. ## What to Avoid The mineral is sensitive to acids, which can damage it. Contact with household and laboratory chemicals should be avoided. It should also not be heated or exposed to sudden temperature changes. Prolonged exposure to direct sunlight is not recommended, although there is no evidence of fading. ## Storage Wöhlerite specimens, especially those with well-formed crystals, should be stored in separate, padded boxes to protect them from impacts and scratching by harder minerals. Due to their brittleness and cleavage, they should be handled gently.