Monteregianite-(Y)

Chemical formula: KNa₂YSi₈O₁₉·5H₂O

Monteregianite-(Y) is a rare yttrium, sodium, and potassium silicate, forming colorless or white, prismatic crystals, discovered at the famous Mont Saint-Hilaire locality in Canada.

## Characteristics Monteregianite-(Y) is a hydrated silicate from the rhodesite group, containing yttrium, sodium, and potassium. This mineral typically forms small, elongated, prismatic crystals, often gathered into radial or fibrous aggregates. Specimens can be transparent to opaque, and their surfaces often exhibit a vitreous luster. ## Physical Properties Monteregianite-(Y) is a relatively soft mineral with a Mohs hardness of 3.5. Its density is 2.42 g/cm³, making it quite light. It is characterized by perfect cleavage in one direction and very good cleavage in another, which makes it brittle and delicate. The luster is typically vitreous. ## Colors and Varieties The most common specimens are colorless, white, or gray. Less frequently, this mineral takes on a pale violet (lavender) or pale green color. No named varieties are distinguished. ## History and Name The mineral's name refers to the Monteregian Hills in Quebec, Canada, where its type locality is situated. The "-(Y)" suffix in the name indicates the dominance of yttrium in its chemical composition. It was first described in 1973 by Joseph A. Mandarino, Guy Perrault, and Donald C. Harris. ## Applications Due to its rarity and small crystal size, monteregianite-(Y) has no industrial applications. It is solely a mineral of scientific and collector's interest, sought after by specialists collecting minerals from Mont Saint-Hilaire.

Properties

Mohs hardness
3.5
Luster
Vitreous
Streak
White
Density
2.42
Cleavage
{010} perfect, {001} very good,{100} fair.
Fracture
Uneven
Transparency
Transparent,Translucent,Opaque
Crystal system
Monoclinic

Diagnostic features

## Identification Monteregianite-(Y) can be identified by its characteristic, elongated, prismatic crystals, often forming radial aggregates. Key features include low hardness (3.5), vitreous luster, and perfect cleavage. Its occurrence in nepheline syenites at Mont Saint-Hilaire is a strong diagnostic indicator. ## Distinguishing from Similar Minerals It can be confused with other white, fibrous zeolite minerals or silicates found in the same locality, such as natrolite or ekanite. It differs from natrolite in crystal habit and lower hardness. Accurate identification often requires advanced analytical methods, such as X-ray diffraction (XRD). ## Crystal Forms Crystals are monoclinic, prismatic in habit, elongated along one axis. They often occur as radial or fibrous aggregates, as well as rosettes or spherulitic aggregates of fine needles.

Geological environment

## Genesis Monteregianite-(Y) is a hydrothermal mineral. It forms in the late stages of crystallization within vugs and fractures in nepheline syenites and associated pegmatites and xenoliths. It is a product of low-temperature alteration processes. ## Mineral Associations This mineral co-occurs with a wide range of other rare minerals characteristic of Mont Saint-Hilaire. The most common associations include: microcline, nepheline, aegirine, natrolite, analcime, serandite, eudialyte, as well as rarer species like lemoynite or leifite. ## Localities The most important and best-known occurrence of monteregianite-(Y) is its type locality – the Poudrette quarry on Mont Saint-Hilaire in Quebec, Canada. This is a world-renowned mineralogical site, known for over 400 different minerals. Beyond Canada, its presence has also been reported in the Pilanesberg alkaline complex in South Africa.

Rarity

Very rare

For collectors

## Quality Criteria Most valued by collectors are specimens with well-formed, sharp, and transparent crystals, forming aesthetic, radial aggregates. Rare specimens with pale violet or greenish coloration are particularly sought after. A contrasting association with other Mont Saint-Hilaire minerals, such as dark green aegirine or orange serandite, significantly enhances the specimen's attractiveness. ## Popular Localities The vast majority, if not all, specimens available on the collector's market come from one place in the world: the Poudrette quarry at Mont Saint-Hilaire in Quebec, Canada. This is the classic locality for this mineral, and specimens from there are the benchmark for the species.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using a soft brush to remove dust. Distilled water can be used, but prolonged soaking should be avoided. Due to its perfect cleavage, mechanical or ultrasonic cleaning is highly inadvisable. ## What to Avoid Contact with acids and other chemicals should be avoided. The mineral is brittle and sensitive to impacts and scratches. It should not be exposed to high temperatures, which can cause the loss of water from its structure and crystal damage. ## Storage Monteregianite-(Y) specimens should be stored in separate, padded boxes to protect them from mechanical damage and contact with harder minerals. They should be protected from dust and direct sunlight.

External references

Sources

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