Donnayite-(Y)

Chemical formula: NaSr₃CaY(CO₃)₆·₃H₂O

Donnayite-(Y) is a rare carbonate mineral, forming characteristic, pseudohexagonal crystals with a yellowish hue.

## Characteristics Donnayite-(Y) is a hydrated carbonate of sodium, strontium, calcium, and yttrium. This mineral forms characteristic, tabular or prismatic crystals, which often occur as pseudohexagonal, cyclic twins, resembling hexagonal plates or short columns. Crystals are usually small, rarely exceeding a few millimeters. They typically appear as single, well-formed crystals or in small groups grown on other minerals. ## Physical Properties Crystals are brittle and exhibit a vitreous luster on faces, and a slightly more resinous luster on fracture surfaces. The mineral is relatively soft, with a Mohs hardness of about 3. It is translucent to transparent. Its density is higher than average for carbonates, approximately 3.3 g/cm³. ## Colors and Varieties Donnayite-(Y) most commonly ranges in color from pale yellow to yellowish-brown. Colorless, whitish, gray, and even pinkish or reddish-brown specimens are also found. Some crystals may exhibit color zoning, with a darker core and lighter outer zones. No named varieties are distinguished. ## History and Name The mineral was discovered in the De-Mix quarry in Mont Saint-Hilaire (Quebec, Canada) and described in 1978 by a team of mineralogists: Guy Perrault, Joseph T. Szymański, and John F. Rowland. The name honors Joseph Désiré Hubert Donnay (1895–1994) and his wife Gabrielle Donnay (1920–1987), professors of crystallography at McGill University and Johns Hopkins University, for their contributions to the development of this field of science. The suffix "-(Y)" in the name indicates the dominance of yttrium (Y) in the chemical composition, in accordance with the rules for naming minerals with rare earth elements. ## Uses Donnayite-(Y) has no industrial applications. It is solely a mineral of scientific and collector's interest, sought after for its rarity and interesting crystallography.

Properties

Mohs hardness: 3
Color: pale yellow to yellow, colorless, white, grey, brown to reddish brown
Luster: Vitreous, Resinous
Streak: White
Density: 3.30
Cleavage: Basal cleavage indistinct to fair
Fracture: Conchoidal
Transparency: Transparent
Crystal system: Triclinic

Diagnostic features

## Identification A key diagnostic feature of Donnayite-(Y) is its characteristic crystallographic form – pseudohexagonal, tabular or prismatic crystals, which are actually cyclic twins. Other helpful identification features include its yellowish color, vitreous luster, relatively low hardness, and vigorous reaction with acids. This mineral often occurs in vugs within nepheline syenites. ## Distinguishing from Similar Minerals Donnayite-(Y) can be confused with other carbonates from the burbankite group, such as ewaldite or mckelveyite-(Y), which form similar pseudohexagonal crystals. Distinguishing these minerals without advanced analytical methods (e.g., X-ray diffraction or chemical analysis) is practically impossible. Analysis of associated minerals, typical for a given location, may be helpful. ## Crystal Forms Crystals are trigonal, but almost always occur as six-fold cyclic twins, which gives them a distinct pseudohexagonal appearance. Most commonly, they form thin or thick hexagonal plates, as well as short hexagonal prisms. Rosette-like aggregates or spherulites are less common.

Geological environment

## Genesis Donnayite-(Y) is a hydrothermal mineral, crystallizing in the late stages of the evolution of alkaline rock complexes, especially nepheline syenites and associated pegmatites. It forms in vugs and druses, often within altered xenoliths (fragments of foreign rocks) within alkaline intrusions. ## Mineral Associations This mineral co-occurs with a wide range of other rare minerals typical of alkaline environments. In its type locality (Mont Saint-Hilaire), its associated minerals include analcime, aegirine, microcline, nepheline, natrolite, ewaldite, mckelveyite-(Y), sericite, catapleiite, and sydorenkite. In Khibiny (Russia), it occurs with natrolite, aegirine, thermonatrite, trona, and shortite. ## Localities The most important and type locality for Donnayite-(Y) is the Mont Saint-Hilaire alkaline complex in Quebec, Canada, from which the world's best specimens originate. It is also known from alkaline massifs on the Kola Peninsula in Russia, particularly Khibiny (Oleniy Ruchey mine) and Lovozero. Other confirmed localities include the Ilimaussaq complex in Greenland.

Rarity

Rare

For collectors

## Quality Criteria The most prized by collectors are specimens from Mont Saint-Hilaire, which are characterized by sharp, well-formed, pseudohexagonal crystals with an intense, honey-yellow color and good transparency. Aesthetic compositions where Donnayite-(Y) crystals contrast with a light background, for example, with white analcime or natrolite, are also highly valued. Crystal size is a key factor – specimens exceeding 5 mm are already considered exceptional. ## Popular Localities By far the most sought-after and classic locality for this mineral is Mont Saint-Hilaire in Canada. Specimens from there set the standard against which others are compared. Crystals from the Russian Khibiny and Lovozero massifs, although also valued, generally fall short of Canadian ones in terms of form and aesthetics.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using a soft brush to remove dust. Brief rinsing in distilled water is permissible, followed by immediate and thorough drying. Due to its solubility in acids, all chemical cleaning agents should be avoided. ## What to Avoid The mineral is sensitive to acids, in which it reacts vigorously (effervesces), releasing carbon dioxide. Contact with hydrochloric acid, sulfuric acid, and other common chemicals should be avoided. It is brittle, so it should be protected from impacts and vibrations. It should not be heated or subjected to ultrasound. ## Storage Donnayite-(Y) specimens are best stored in separate, padded display boxes to prevent scratches and mechanical damage. They should be protected from dust and moisture. Due to the small size of the crystals, they are often stored in special boxes with a magnifying glass (so-called micromounts).