Lecoqite-(Y)

Chemical formula: Na₃Y(CO₃)₃(H₂O)₆

Lecoqite-(Y) is a rare, hydrated sodium and yttrium carbonate, forming colorless, acicular crystals, discovered in the famous Mont Saint-Hilaire quarry in Canada.

## Characteristics Lecoqite-(Y) is a hydrated sodium and yttrium carbonate, belonging to the group of rare minerals. It occurs as fine, acicular or hair-like crystals, which can form radial aggregates or tangled, wool-like masses. Individual crystals are usually very small, reaching up to 1 mm in length and only a few micrometers in thickness. Due to its habit and small size, it is a mineral difficult to observe without magnification. ## Physical Properties Lecoqite-(Y) crystals are transparent and exhibit a vitreous luster. The mineral's density is approximately 2.36 g/cm³. Its fracture is splintery, which is typical for minerals with a fibrous structure. Hardness has not been precisely determined, but given its composition and structure, it can be assumed to be a relatively soft and brittle mineral. ## Colors and Varieties Lecoqite-(Y) is most often colorless or white. No colored varieties or trade names are known. ## History and Name The mineral was officially recognized by the International Mineralogical Association (IMA) in 2010 under number IMA2010-011. Its name honors Anette Lecoq (born 1961), a Belgian mineral collector who found the first samples of this mineral. The suffix "-(Y)" in the name indicates the dominant rare earth element in its composition – yttrium. ## Uses Lecoqite-(Y) has no industrial application. Its significance is purely scientific and collector-oriented, as a rare and well-defined representative of the rare earth carbonate group.

Properties

Luster
Vitreous
Streak
White
Density
2.358
Fracture
Splintery
Transparency
Transparent
Crystal system
Hexagonal

Diagnostic features

## Identification Lecoqite-(Y) can be identified by its characteristic mode of occurrence – as very fine, acicular or hair-like crystals, often forming radial or tangled aggregates. Colorless or white color, vitreous luster, and occurrence in a specific geological environment (pegmatites in nepheline syenites) are key features. Final identification requires advanced analytical methods, such as Raman spectroscopy or X-ray diffraction. ## Distinguishing from Similar Minerals This mineral can be confused with other acicular, white minerals found at Mont Saint-Hilaire, such as natrolite, ancylite, or some zeolites. Lecoqite-(Y) differs from them in chemical composition (it is a carbonate, not a silicate) and reaction to water (it is soluble). Compared to the similar carbonate mckelveyite-(Y), lecoqite-(Y) has a different chemical composition and crystal structure. ## Crystal Forms Crystals are elongated, acicular or hair-like, with a hexagonal cross-section. They usually occur as radial aggregates growing from a single base or as tangled, woolly masses filling small voids in the rock.

Geological environment

## Genesis Lecoqite-(Y) is a secondary mineral, formed in the late stage of hydrothermal processes. It crystallizes at low temperatures in voids and fractures within syenite pegmatites, which are part of the Mont Saint-Hilaire alkaline intrusion. ## Mineral Associations This mineral co-occurs with many other rare minerals from Mont Saint-Hilaire. At the type locality, it was found in association with mckelveyite-(Y), donnayite-(Y), ewaldite, analcime, microcline, aegirine, cancrinite, sodalite, catapleiite, and petersenite-(Ce). ## Localities The only confirmed locality of lecoqite-(Y) in the world is its type locality – the Poudrette quarry in the Mont Saint-Hilaire complex, Montérégie region, Quebec province, Canada. This is one of the most famous mineralogical sites in the world, known for the occurrence of over 400 different mineral species.

Rarity

Very rare

For collectors

## Quality Criteria The most prized lecoqite-(Y) specimens are those that display well-formed, radial aggregates of acicular crystals on a contrasting rock matrix. The size and richness of the clusters, as well as the absence of damage to the delicate needles, are important. Due to the microscopic size of the crystals, specimens are primarily evaluated under magnification. Association with other rare minerals from Mont Saint-Hilaire also increases the collector's value of the specimen. ## Popular Localities The only source of lecoqite-(Y) specimens is the Poudrette quarry in Mont Saint-Hilaire, Canada. Specimens from this locality are the standard for this mineral and the only ones available on the collector's market.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using compressed air to remove dust. Due to extreme brittleness and water solubility, any contact with liquids and mechanical cleaning (e.g., with brushes) should be avoided. ## What to Avoid Contact with water and other liquids, which can dissolve or damage the delicate crystals, must be absolutely avoided. The mineral is sensitive to acids. It should be protected from shocks, impacts, and abrasion. Store away from heat sources and sudden temperature changes. ## Storage It is recommended to store specimens in sealed, closed "micromount" boxes, which protect against dust, moisture, and mechanical damage. Display should take place under stable conditions, away from direct sunlight and sources of vibration.

External references

Sources

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