Lemoynite
Chemical formula: Na<sub>2</sub>CaZr<sup>4+</sup><sub>2</sub>Si<sub>10</sub>O<sub>26</sub>·5-6H<sub>2</sub>O
Lemoynite is a very rare silicate mineral, prized for its delicate, fibrous, pale yellow crystals found in nepheline syenites.
Properties
- Mohs hardness
- 4
- Luster
- Vitreous to Silky
- Streak
- White
- Density
- 2.69
- Cleavage
- Perfect on {100} and {010}
- Fracture
- Uneven
- Transparency
- Translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Characteristic features of lemoynite include its pale yellow color, fibrous appearance, and the formation of radial aggregates. The locality is also crucial – the vast majority of specimens come from Mont Saint-Hilaire. It occurs in vugs within nepheline syenites. ## Distinguishing from Similar Minerals Lemoynite can be confused with other fibrous, yellow minerals from Mont Saint-Hilaire, such as monteregianite-(Y) or some zeolites. However, monteregianite-(Y) is soluble in acids, and precise differentiation often requires advanced analytical methods, such as X-ray diffraction (XRD). ## Crystal Forms The mineral forms fine, acicular to fibrous crystals, which almost always occur as radial or spherulitic aggregates and rosettes. Single, well-formed crystals are practically nonexistent.
Geological environment
## Genesis Lemoynite is a hydrothermal mineral. It crystallizes in the late stage from post-magmatic solutions in vugs and fissures of syenite pegmatites and xenoliths within alkaline intrusions, such as nepheline syenites. ## Mineral Associations It most commonly co-occurs with minerals typical of the Mont Saint-Hilaire environment, such as analcime, microcline, aegirine, natrolite, as well as other rare zirconium and titanium minerals, e.g., monteregianite-(Y), elpidite, or sérandite. ## Localities The most important and historical occurrence of lemoynite is the Mont Saint-Hilaire massif in Quebec, Canada, which is its type locality. It has also been found in the Pilanesberg alkaline complex in the Republic of South Africa and in the Khibiny massif on the Kola Peninsula in Russia. Nevertheless, specimens from Mont Saint-Hilaire remain the standard for this mineral.
Rarity
Very rare
For collectors
## Quality Criteria The most sought-after lemoynite specimens are those with well-defined, spherical aggregates of intense, canary-yellow color, contrastingly set on a light rock matrix (e.g., on analcime). The absence of damage to the delicate fibers and the aesthetic arrangement of the clusters are important. Specimens with larger aggregate diameters (above 5 mm) are significantly more valuable. ## Popular Localities Specimens from the Poudrette and Demix quarries in Mont Saint-Hilaire, Quebec, Canada, are by far the most prized and commonly found on the collector's market. Material from other localities is extremely rare and represents a great find for specialized collectors.
Care and storage
## Cleaning Lemoynite specimens are extremely delicate and fragile. Any mechanical cleaning, including the use of brushes, should be avoided. If absolutely necessary, compressed air can be carefully used from a safe distance to remove loose dust. ## What to Avoid Avoid contact with water and any chemicals that could damage the delicate fibers or the host rock. The mineral is sensitive to shocks and impacts. Prolonged exposure to strong sunlight may potentially cause fading, although this is not well documented. ## Storage It is recommended to store specimens exclusively in sealed "micromount" boxes, which protect against dust, mechanical damage, and sudden changes in humidity. Avoid placing heavy objects on the box.