Varulite

Chemical formula: Na₂Mn₂+(Mn₂+Fe₃+)(PO₄)₃

Varulite is a rare phosphate mineral, forming granular aggregates with a characteristic olive-green to brownish color.

## Characteristics Varulite is a complex sodium, manganese, and iron phosphate, belonging to the alluaudite group. It rarely forms distinct crystals, most often occurring as granular or massive aggregates, strongly intergrown with the rock. Its appearance is usually inconspicuous, and specimens most often take the form of masses embedded in rock with a dull or slightly vitreous luster. ## Physical Properties This mineral is characterized by a hardness of 5 on the Mohs scale, placing it in the same category as apatite. It is relatively brittle. Its density is greater than that of quartz, approximately 3.5-3.6 g/cm³. The luster is most often vitreous, sometimes dull or resinous on fracture surfaces. ## Colors and Varieties The typical color of varulite is olive-green, which can transition to greenish-brown, yellowish-brown, and even blackish-brown shades due to oxidation. No named varieties are distinguished. ## History and Name The mineral's name comes from its type locality – the Varuträsk farm in Sweden, where it was first found. It was described by Percy Quensel and Thure Georg Sahama in 1937. It is the sodium analogue of hagendorfite. ## Uses Varulite has no industrial applications. Its significance is purely scientific and as a collector's item, as a rare member of the alluaudite group.

Properties

Mohs hardness: 5
Luster: Vitreous to resinous
Streak: Greenish gray
Density: 3.5-3.6
Cleavage: Good on {010}
Fracture: Uneven
Transparency: Translucent to opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Identifying varulite in the field is difficult. Key features include its olive-green color, granular habit, and mineral associations typical of granitic pegmatites. It exhibits good cleavage in one direction. Final confirmation requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical analysis. ## Distinguishing from Similar Minerals Varulite can be confused with other phosphates of similar color and habit, such as triphylite, lithiophilite (especially their oxidized forms), arrojadite, or rockbridgeite. Distinguishing them without specialized equipment is practically impossible. Knowledge of paragenesis and locality is helpful. ## Crystal Forms Well-formed crystals are extremely rare. It usually occurs as granular, massive aggregates embedded in the host rock. Crystals, if they appear, are tabular or prismatic and reach small sizes.

Geological environment

## Genesis Varulite is a mineral of primary or secondary origin in complex granitic pegmatites, rich in lithium and phosphorus. It forms as a result of crystallization from residual post-magmatic fluids or through sodium metasomatism, acting on previously crystallized phosphates such as triphylite-lithiophilite. ## Mineral Associations This mineral often co-occurs with other phosphates, such as triphylite, lithiophilite, arrojadite-(KFe), alluaudite, as well as with quartz, feldspars (albite, microcline), muscovite, and other pegmatite minerals. ## Localities The most important and classic varulite localities are the Varuträsk pegmatite in Sweden (type locality) and pegmatites in the Black Hills region of South Dakota, USA (e.g., Tip Top mine, White Elephant mine). It is also known from pegmatites in Finland (Viitaniemi), Brazil (Minas Gerais and Paraíba states), and Rwanda.

Rarity

Rare

For collectors

## Quality Criteria The collector's appeal of varulite is limited due to its inconspicuous appearance. The most prized specimens are those with rare, well-formed microcrystals. In the case of massive aggregates, the intensity and purity of the olive-green color, the size of the aggregate, and the richness of associations with other rare phosphates determine its value. ## Popular Localities The most classic and sought-after specimens by collectors come from the type locality in Varuträsk, Sweden, and from the Tip Top mine in South Dakota, USA, where rich aggregates of this mineral are known.

Care and storage

## Cleaning Varulite specimens should only be cleaned mechanically, using a soft, dry brush to remove dust. Due to its potential reactivity, contact with water, and especially with acids and detergents, should be avoided. ## What to Avoid Ultrasonic cleaners should be avoided, as they can damage brittle and fractured aggregates. The mineral is susceptible to oxidation, so it should be protected from moisture and prolonged exposure to air, which can cause darkening and color changes. Contact with chemicals and acids should also be avoided. ## Storage It is recommended to store specimens in dry conditions, preferably in closed collector boxes or display cases with a desiccant. This will protect the mineral from progressive oxidation and degradation.

Sources

IMA Mineral List (CNMNC)