Perraultite

Chemical formula: NaBaMn₂+₄Ti₄+₂(Si₂O₇)₂O₂(OH)₂F

Perraultite is a rare silicate mineral, forming characteristic brown, tabular crystals, primarily known from Mont Saint-Hilaire in Canada.

## Characteristics Perraultite is a complex silicate of titanium, manganese, barium, and sodium, belonging to the bafertisite group. It forms thin to thick tabular crystals, often with pseudohexagonal outlines. These crystals frequently arrange themselves into fan-shaped, radial, or spherical aggregates and rosettes. It is a brittle mineral, exhibiting perfect, unidirectional cleavage. ## Physical Properties The hardness of perraultite on the Mohs scale is approximately 4, making it a relatively soft mineral. It has a vitreous luster, transitioning to resinous on fracture surfaces. It is translucent, and in thicker fragments, opaque. Its density is quite high, around 3.99 g/cm³. ## Colors and Varieties This mineral occurs in shades of brown – from yellowish-brown, through reddish-brown, to dark brown. No named color varieties or commercial variants are distinguished. ## History and Name Perraultite was described in 1998 by George Y. Chao, Joel D. Grice, and Robert A. Gault. The name honors Jacques Perrault (b. 1927), a Canadian mining engineer and mineral collector, who specialized in specimens from Mont Saint-Hilaire. The type locality is the Poudrette quarry in Mont Saint-Hilaire, Quebec, Canada. ## Uses Perraultite has no industrial applications. It is solely an object of scientific interest and a prized acquisition for advanced mineralogical collections.

Properties

Mohs hardness: 4
Luster: Vitreous to Resinous
Streak: Pale brown
Density: 3.99
Cleavage: Perfect on {001}
Fracture: Uneven
Transparency: Translucent to Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Characteristic features of perraultite include its brown color, tabular crystal habit often forming radial aggregates, and perfect cleavage. Its paragenesis, i.e., its occurrence in association with other rare alkaline pegmatite minerals, is also crucial. ## Distinguishing from similar minerals Perraultite is visually almost indistinguishable from other minerals in its group, such as jinshajiangite or bafertisite. Jinshajiangite is often more orange or golden-brown, but a definitive distinction requires advanced analytical methods (e.g., EDS, XRD). It is distinguished from similarly looking micas (e.g., biotite) by its significantly higher density and specific occurrence environment. ## Crystal forms Most commonly, tabular, bladed crystals are found, which combine into fan-shaped, radial, or spherical aggregates. Single, well-formed crystals are rare.

Geological environment

## Genesis Perraultite is a hydrothermal mineral, crystallizing in the late stages of the formation of nepheline-syenite pegmatites. It occurs in rock fissures and vugs, often within marble xenoliths altered by metasomatic processes. ## Mineral associations At the type locality (Mont Saint-Hilaire), it co-occurs with many other, often rare minerals, such as aegirine, albite, microcline, nepheline, sodalite, eudialyte, serandite, and lorenzenite. ## Localities The most important locality, providing the world's best specimens, is the Poudrette quarry, Mont Saint-Hilaire in Quebec, Canada. Its presence has also been noted in the alkaline massifs of the Kola Peninsula in Russia (Khibiny and Lovozero).

Rarity

Very rare

For collectors

## Quality criteria The most highly valued perraultite specimens are those with sharply defined, well-formed crystals creating aesthetic rosettes or fans. Intense, saturated color and good luster increase its value. Compositions where brown perraultite crystals contrast with a light matrix, such as white albite or green aegirine, are particularly desirable. ## Popular localities By far the most sought-after and classic specimens come from the only place in the world where they occur in great abundance and excellent quality – the Poudrette quarry in Mont Saint-Hilaire, Canada.

Care and storage

## Cleaning Perraultite specimens should be cleaned very carefully, preferably with a soft brush dry. If necessary, distilled water can be used, applied gently and the specimen immediately dried. ## What to avoid The mineral is very brittle and has perfect cleavage, so any impacts, pressure, and vibrations should be avoided. The use of ultrasonic cleaners is absolutely forbidden. It should be protected from contact with acids and other strong chemicals. ## Storage It is recommended to store specimens in separate, padded boxes, away from harder minerals that could scratch it. It is not particularly sensitive to light, but for safety, it is better to avoid prolonged exposure to direct sunlight.

Sources

IMA Mineral List (CNMNC)