Gaidonnayite

Chemical formula: Na₂Zr₄+Si₃O₉·₂H₂O

Gaidonnayite is a rare zirconium and sodium silicate, forming colorless or white crystals with a vitreous luster, prized by mineral collectors.

## Characteristics Gaidonnayite is a rare, hydrated zirconium and sodium silicate. It typically forms small, prismatic or tabular crystals, which can occur as radial or spherulitic aggregates. It is most commonly colorless, white, or pale yellow. Due to its rarity and attractive crystalline forms, it is an interesting specimen for advanced collectors. ## Physical Properties Gaidonnayite crystals are characterized by a vitreous luster, and on cleavage surfaces, they may exhibit a pearly luster. This mineral is transparent to translucent. Its Mohs hardness is 5, and its density ranges from 2.94-2.98 g/cm³. ## Colors and Varieties Gaidonnayite occurs in a limited color range. Colorless and white specimens dominate, with pale yellow or cream-colored ones being rarer. No named varieties are distinguished. ## History and Name The mineral was discovered at Mont Saint-Hilaire in Quebec, Canada, and described in 1974. Its name honors Gabrielle Donnay (1920-1987), a crystallographer at McGill University in Montreal, for her contributions to mineralogy and crystallography, including her research on minerals from Mont Saint-Hilaire. ## Uses Gaidonnayite has no industrial applications. Its significance is purely scientific and collectible.

Properties

Mohs hardness: 5
Luster: Vitreous, Pearly
Streak: White
Density: 2.94-2.98
Cleavage: Good on {110}
Fracture: Uneven
Transparency: Transparent to translucent
Crystal system: Orthorhombic

Diagnostic features

## Identification Characteristic features of gaidonnayite include its crystal forms – prismatic crystals often grouped into radial aggregates – and its occurrence in a specific geological environment (nepheline syenites). Vitreous luster and relatively low hardness (5 on the Mohs scale) are also helpful in identification. ## Distinguishing from Similar Minerals Gaidonnayite can be confused with other colorless or white minerals from its paragenesis, such as natrolite or analcime. It differs from natrolite in crystal form (natrolite forms acicular crystals) and hardness. It is distinguished from analcime by a different crystallographic system (analcime is isometric) and crystal habit. Final differentiation often requires advanced research methods, such as X-ray diffraction. ## Crystal Forms Gaidonnayite crystals are usually small, prismatic in habit, often elongated and terminated by pyramids. It forms characteristic radial or fan-shaped aggregates, as well as spherulites and rosettes composed of tiny crystals.

Geological environment

## Genesis Gaidonnayite is a hydrothermal mineral, crystallizing in the late stages of the evolution of alkaline massifs, especially nepheline syenites. It forms in vugs, miarolitic cavities, and rock fractures, often within syenite pegmatites. ## Mineral Associations This mineral co-occurs with a wide range of other rare alkaline minerals. Its most common associations include: analcime, natrolite, aegirine, microcline, nepheline, catapleiite, elpidite, hilairite, and serandite. ## Localities The most important and classic locality for gaidonnayite is Mont Saint-Hilaire in Quebec, Canada, which has yielded the world's best specimens. It is also known from the Kola Peninsula in Russia (Khibiny and Lovozero massifs) and the Ilimaussaq igneous complex in Greenland. These are the only confirmed, significant localities for this mineral.

Rarity

Rare

For collectors

## Quality Criteria The most highly valued gaidonnayite specimens are those with well-formed, sharp, and transparent crystals. Radial aggregates of aesthetic shape, forming "sunbursts" or fans, are particularly sought after. Contrasting placement on a rock matrix, especially in association with other rare minerals (e.g., colorful serandite), significantly increases the specimen's value. The size of crystals and aggregates is also a key factor. ## Popular Localities By far the most desired specimens by collectors come from the type locality – Mont Saint-Hilaire in Quebec, Canada. This locality has provided the largest and best-formed crystals of this mineral.

Care and storage

## Cleaning Gaidonnayite specimens should be cleaned very carefully, using a soft brush to remove dust. If necessary, distilled water can be used, but prolonged soaking should be avoided. Always dry the specimen thoroughly after cleaning. ## What to Avoid Avoid contact with acids and other aggressive chemicals. The mineral is relatively soft, so it must be protected from scratching by harder minerals. It should not be heated or subjected to ultrasound, as this can cause damage. ## Storage Gaidonnayite specimens are best stored in individual, padded display boxes to prevent abrasion and mechanical damage. They should be protected from dust and sudden temperature changes.

Sources

IMA Mineral List (CNMNC)