Gaultite

Chemical formula: Na₄Zn₂+₂Si₇O₁₈·₅H₂O

Gaultite is a rare sodium zinc silicate, forming colorless or white crystals with a characteristic columnar or acicular habit.

## Characteristics Gaultite is a mineral from the silicate group, which crystallizes as slender, elongated crystals with a square or rectangular cross-section. It usually occurs as colorless or white, forming radial aggregates or groups of scattered, acicular crystals on the surface of the host rock. Individual crystals are often transparent and exhibit a vitreous luster, which gives them an attractive appearance, especially in druses. ## Physical Properties This mineral is characterized by a hardness ranging from 5-6 on the Mohs scale. Its crystals are brittle, and their luster is described as vitreous. It is transparent to translucent. The density of gaultite is approximately 2.45 g/cm³. ## Colors and Varieties Gaultite is typically colorless or white. No colored varieties or trade names have been described, which is due to its rarity and lack of applications beyond collecting and scientific study. ## History and Name The mineral is named in honor of Robert Alan Gault (born 1944), a Canadian mineralogist and curator of collections at the Canadian Museum of Nature in Ottawa, in recognition of his contributions to mineralogy, particularly in the study of minerals from Mont Saint-Hilaire. Gaultite was described as a new mineral species in 1994. ## Uses Due to its rarity and small crystal size, gaultite has no industrial applications. It is exclusively a mineral of scientific and collector's importance, sought after by specialists and advanced collectors of rare species.

Properties

Mohs hardness: 5-6
Luster: Vitreous
Streak: White
Density: 2.45
Cleavage: Good on {100} and {010}
Fracture: Uneven
Transparency: Transparent to translucent
Crystal system: Orthorhombic

Diagnostic features

## Identification The diagnosis of gaultite is based on its characteristic habit – slender, elongated crystals with a square cross-section, often forming radial aggregates. Important features also include vitreous luster, colorless or white color, and occurrence in a specific geological environment (alkaline intrusions). ## Distinguishing from Similar Minerals Gaultite can be confused with other acicular zeolites or silicates, such as natrolite or edingtonite, which also occur at Mont Saint-Hilaire. Differentiation often requires advanced research methods, such as X-ray diffraction (XRD) or chemical analysis (EDS), due to the similarity of crystal forms and physical properties. ## Crystal Forms Gaultite crystals are columnar or acicular, elongated along the crystallographic axis. They usually have a square or rectangular cross-section. They form radial or chaotically arranged aggregates, as well as individual, grown crystals in rock cavities.

Geological environment

## Genesis Gaultite is a hydrothermal mineral, crystallizing in the late stage of alkaline magma evolution. It forms in cavities and fractures within nepheline syenites and associated pegmatites, under low-temperature conditions. ## Mineral Associations This mineral occurs in association with other rare minerals typical of alkaline intrusions. In its type locality (Mont Saint-Hilaire), it co-occurs with analcime, aegirine, microcline, catapleiite, edingtonite, and natrolite. ## Localities The most important and also the type locality for gaultite is the Poudrette quarry at Mont Saint-Hilaire, in the Montérégie region of Quebec, Canada. This is a world-renowned locality for rare alkaline minerals. Outside of Canada, its presence has also been reported in the Wind Mountain alkaline complex in Otero County, New Mexico, USA.

Rarity

Very rare

For collectors

## Quality Criteria The most highly prized gaultite specimens are characterized by sharply terminated, transparent crystals with a distinct luster, grouped into aesthetic, radial aggregates. The size of individual crystals is also important – the longer and better-formed they are, the more valuable the specimen. Contrast with the color of the host rock (matrix) and the absence of damage significantly increase collector appeal. ## Popular Localities Undoubtedly, the most desired and classic gaultite specimens come from its discovery site – the Poudrette quarry at Mont Saint-Hilaire in Canada. Specimens from this locality are the benchmark for this mineral.

Care and storage

## Cleaning Careful cleaning with a soft, dry brush is recommended to remove dust. If necessary, compressed air can be used from a safe distance. Avoid washing with water, which can leave deposits or penetrate microfractures. ## What to Avoid Avoid contact with acids and strong chemical agents. The crystals are brittle and sensitive to impacts and vibrations. Do not subject the specimen to ultrasonic cleaners or steam cleaning. ## Storage Gaultite specimens, being brittle and often occurring on a delicate matrix, should be stored in stable conditions, in sealed collector boxes that protect them from dust, mechanical damage, and sudden temperature changes.

Sources

IMA Mineral List (CNMNC)