Haineaultite

Chemical formula: (Na,Ca)₅Ca(Ti₄+,Nb₅+)₅Si₁₂O₃₄(OH,F)₈·₅H₂O

Hainaultite is a rare mineral from the silicate group, distinguished by its unique chemical composition containing niobium and titanium, and its occurrence as small, radial aggregates.

## Characteristics Hainaultite is a complex silicate of sodium, calcium, titanium, and niobium, belonging to the zorosilicates group. It forms very small, acicular or bladed crystals, which most often occur as spherical or radial aggregates. Individual crystals rarely exceed 1 mm in length. Due to its size and mode of occurrence, it is a mineral of interest mainly to advanced micromounters. ## Physical Properties Hainaultite crystals exhibit a vitreous luster. They are transparent to translucent. The Mohs hardness is approximately 5, and the density is slightly higher than quartz, approximately 2.76 g/cm³. ## Colors and Varieties This mineral is usually colorless or has a pale yellow, and sometimes greenish-yellow hue. No named varieties have been distinguished. ## History and Name The mineral's name comes from its type locality – the Poudrette quarry at Mont Saint-Hilaire in Quebec, Canada, which is located in the regional municipality of La Vallée-du-Richelieu, formerly known as Haineault. It was described and approved as a new mineral species by the International Mineralogical Association (IMA) in 1997. ## Uses Due to its rarity and microscopic crystal sizes, hainaultite has no industrial applications. It is solely an object of collector interest, especially for specialists in minerals from Mont Saint-Hilaire.

Properties

Mohs hardness: 5
Luster: Vitreous
Streak: White
Density: 2.76
Cleavage: Good on {100} and {010}
Fracture: Uneven
Transparency: Transparent to Translucent
Crystal system: Orthorhombic

Diagnostic features

## Identification Identification of hainaultite is primarily based on its characteristic mode of occurrence – spherical or radial aggregates composed of small, acicular crystals. The locality is also crucial; this mineral is almost exclusively associated with the alkaline intrusive complex of Mont Saint-Hilaire. Positive identification requires advanced analytical methods, such as EDS/WDS spectroscopy, to confirm its unique chemical composition with the presence of Ti and Nb. ## Distinguishing from Similar Minerals It can be confused with other acicular silicates found at Mont Saint-Hilaire, such as aegirine, elpidite, or some zeolites. Hainaultite differs from them by the habit of its aggregates (often spherical), its specific pale yellow color, and its chemical composition. Unlike many zeolites, it does not react with hydrochloric acid. ## Crystal Forms Crystals are elongated, acicular or bladed, with a cross-section similar to a square. They usually form radial, stellate, or spherical aggregates. Less commonly, they are found as chaotically arranged clusters.

Geological environment

## Genesis Hainaultite is a hydrothermal mineral, crystallizing in the late stage of the evolution of highly differentiated, alkaline nepheline-syenite intrusions. It forms in cavities and rock fissures, often within syenite pegmatites or in altered xenoliths. ## Mineral Associations Minerals co-occurring with hainaultite at the type locality (Mont Saint-Hilaire) include albit, microcline, nepheline, aegirine, sodalite, eudialyte, catapleiite, elpidite, sérandite, and rare niobium and titanium minerals. ## Localities The only confirmed and well-documented locality for hainaultite in the world is the Mont Saint-Hilaire alkaline complex in Quebec, Canada. This is its type locality and the main source of collector specimens.

Rarity

Very rare

For collectors

## Quality Criteria The most prized hainaultite specimens are those with well-formed, spherical aggregates featuring a distinct, radial arrangement of acicular crystals. An intense, pale yellow color and contrast with the surrounding rock matrix are important. Specimens where hainaultite co-occurs with other rare minerals from Mont Saint-Hilaire, forming aesthetic micro-combinations, are also highly valued. ## Popular Localities The only source of specimens is the Poudrette quarry at Mont Saint-Hilaire in Quebec (Canada). Specimens from this locality are the standard for this mineral.

Care and storage

## Cleaning Hainaultite specimens should be cleaned very carefully, preferably using compressed air to remove dust. Avoid contact with water if the mineral occurs on a sensitive matrix. Any mechanical cleaning (brushes, ultrasonics) is highly risky due to the fragility and small size of the crystals. ## What to Avoid Avoid contact with acids and other chemicals. The mineral is brittle, so protect it from impacts and vibrations. Do not heat it or expose it to sudden temperature changes. ## Storage It is recommended to store specimens in sealed "micromount" boxes, which protect delicate crystals from dust, mechanical damage, and humidity. Display should be away from direct sunlight and heat sources.

Sources

IMA Mineral List (CNMNC)