Rouvilleite
Chemical formula: Na₃Ca₂(CO₃)₃F
Rouvilleite is a rare sodium and calcium carbonate, forming colorless, hexagonal crystals, discovered in the Poudrette quarry in Canada.
Properties
- Mohs hardness
- 3
- Color
- Colorless to pale tan
- Luster
- Vitreous
- Streak
- White
- Density
- 2.67
- Cleavage
- Good on {001} and imperfect on {010}.
- Fracture
- Irregular/Uneven
- Transparency
- Transparent
- Crystal system
- Monoclinic
Diagnostic features
## Identification A key diagnostic feature of rouvilleite is its reaction with acids – it effervesces violently, releasing carbon dioxide. Its hexagonal crystal form, vitreous luster, and occurrence in a specific geological environment (syenite xenoliths in nepheline syenites) are also helpful. ## Distinguishing from Similar Minerals It can be confused with other colorless carbonates found at Mont Saint-Hilaire, such as burbankite or natrite. Differentiation often requires advanced analytical methods, such as Raman spectroscopy or chemical analysis (EDS/WDS), although the characteristic hexagonal habit of the crystals is a good indicator. ## Crystal Forms Rouvilleite crystallizes in the form of thin, hexagonal, tabular crystals. The faces of the hexagonal prism are often striated. It occurs as single crystals embedded in the rock or in small aggregates.
Geological environment
## Genesis Rouvilleite forms under very specific geological conditions. Its typical environment consists of syenite xenoliths (fragments of older rocks) embedded within alkaline intrusions, such as nepheline syenites. It forms in the late stages of crystallization, in the presence of solutions rich in sodium, calcium, carbonates, and fluorine. ## Mineral Associations This mineral co-occurs with many other rare minerals typical of Mont Saint-Hilaire. Its most common associations include: aegirine, microcline, nepheline, sodalite, eudialyte, catapleiite, steacyite, and rare carbonates like burbankite. ## Localities The only confirmed and well-documented occurrence of rouvilleite in the world is the Poudrette quarry on Mont Saint-Hilaire, in the Montérégie region, Quebec, Canada. This is its type locality.
Rarity
Very rare
For collectors
## Quality Criteria The most prized rouvilleite specimens are those with sharply defined, well-formed, and transparent crystals that are clearly visible against a contrasting rock matrix. Due to the small size of the crystals, their perfect form and lack of damage are crucial. Specimens where rouvilleite co-occurs with other rare and aesthetic minerals from Mont Saint-Hilaire are particularly desirable. ## Popular Localities The only source of collectible specimens is its type locality: the Poudrette quarry (Mont Saint-Hilaire) in Canada. Specimens from this location are the standard for this mineral.
Care and storage
## Cleaning Rouvilleite specimens should be cleaned very carefully, using a soft brush to remove dust. Due to its reactivity with acids, all chemical cleaning agents should be avoided. If liquid is necessary, pure distilled water or isopropyl alcohol is recommended, applied in minimal amounts and dried quickly. ## What to Avoid Contact with acids must be absolutely avoided, as they cause violent effervescence and decomposition of the mineral. Rouvilleite is relatively soft, so it must be protected from scratching by harder minerals. It should not be heated or exposed to prolonged moisture. ## Storage Due to their small size and fragility, rouvilleite specimens are best stored in enclosed "micromount" boxes, which protect them from mechanical damage and dust. Storage in a humid environment should be avoided.