Varennesite

Chemical formula: Na₈Mn²⁺₂Si₁₀O₂₅(OH,Cl)₂·₁₂H₂O

Warennesite is a very rare mineral from the silicate group, forming unique, spherical aggregates of an orange color.

## Characteristics Warennesite is a hydrated sodium manganese silicate, distinguished by its unique appearance. It typically forms spherical aggregates (spherulites) up to 1 cm in diameter, composed of fine, radially arranged, acicular crystals. Individual crystals are too small to be seen with the naked eye. The aggregates have a characteristic rough surface texture. ## Physical Properties This mineral is relatively soft, with a Mohs hardness of approximately 3. It has a vitreous luster, and due to its aggregate structure, it is usually translucent to opaque. Its density is low, around 2.31 g/cm³. ## Colors and Varieties Warennesite occurs in a characteristic, uniform orange color. No color varieties or commercial varieties are known. ## History and Name The mineral was discovered in the Poudrette quarry at Mont Saint-Hilaire in Quebec, Canada. It was described and approved as a new mineral species in 1996. Its name honors Jean-Michel Varennes (born 1943), a Canadian mineral collector who found the first specimens of this mineral. ## Applications Due to its extreme rarity, warennesite has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals and for scientific institutions.

Properties

Mohs hardness: 4
Color: Pale brownish-yellow to orange
Luster: Vitreous
Streak: White
Density: 2.31
Cleavage: Good {010}
Fracture: Conchoidal
Transparency: Transparent,Translucent
Crystal system: Orthorhombic

Diagnostic features

## Identification The diagnostic feature of warennesite is its unique form of occurrence as orange, spherical aggregates with a radial internal structure. Its characteristic locality is also notable – it occurs almost exclusively in one place in the world. ## Distinguishing from Similar Minerals It can be confused with other spherulitic minerals of orange color, such as some zeolites (e.g., natrolite) or carbonates. Differentiation requires chemical analysis (EDS/WDS) or X-ray diffraction (XRD). However, in the context of the Mont Saint-Hilaire locality, its appearance is specific enough that experienced collectors can identify it visually. ## Crystal Forms It forms spherulitic aggregates composed of microscopic, acicular or bladed crystals arranged radially from a common center.

Geological environment

## Genesis Warennesite is a hydrothermal mineral. It forms in the late stages of crystallization within nepheline syenite pegmatites, crystallizing in voids and rock fractures. Its formation is associated with the activity of sodium and manganese-rich solutions in the alkaline environment of the Mont Saint-Hilaire intrusion. ## Mineral Associations This mineral co-occurs with many other rare minerals typical of Mont Saint-Hilaire, such as aegirine, microcline, analcime, natrolite, catapleiite, eudialyte, sérandite, polylithionite, and steacyite. ## Localities The only confirmed and most important locality for warennesite in the world is the Poudrette quarry at Mont Saint-Hilaire, in the Montérégie region, Quebec province, Canada. This is its type locality.

Rarity

Very rare

For collectors

## Quality Criteria The most prized warennesite specimens are those with well-formed, spherical aggregates of intense orange color and large diameter (above 5 mm). Contrast with the rock matrix on which they occur and the absence of mechanical damage are important. Specimens with multiple spherulites or in association with other rare minerals from this locality are particularly sought after. ## Popular Localities All global supply of collector specimens comes from a single location: the Poudrette quarry at Mont Saint-Hilaire in Canada. Specimens from this locality are considered classics and serve as a reference point for this mineral.

Care and storage

## Cleaning Warennesite specimens should be cleaned very carefully, using a soft brush to remove dust. Due to its softness and possible reactivity, avoid washing it in water, especially with detergents. If it is necessary to remove loose contaminants, compressed air can be used from a safe distance. ## What to Avoid Avoid contact with all chemicals, including acids and bases. The mineral is soft and brittle, so it must be protected from impacts, scratching, and vibrations. It should not be heated or exposed to prolonged strong sunlight. ## Storage Specimens are best stored in individual, padded collector boxes to prevent abrasion and mechanical damage. They should be kept in stable conditions, away from moisture and extreme temperatures.

External references

https://www.mindat.org/min-4155.html