Barwoodite

Chemical formula: Mn₂+₆(Nb₅+,&#₉₇₄₄;)₂(SiO₄)₂(O,OH)₆

Barwoodite is a very rare manganese niobosilicate, forming microscopic, orange-brown crystals in nepheline syenites.

## Characteristics Barwoodite is a mineral from the niobosilicate group, characterized by a complex chemical composition with a dominance of manganese and niobium. It occurs as very small, tabular or lath-like crystals, whose size rarely exceeds 0.3 mm. It typically forms radial or randomly oriented aggregates and clusters. Its crystals are too small to be observed with the naked eye, and their identification requires advanced analytical techniques. ## Physical Properties Barwoodite crystals exhibit a vitreous luster. Due to the microscopic size of the crystals, determining many physical properties, such as hardness or density, is difficult. The hardness is estimated to be around 5 on the Mohs scale, and the density calculated based on the formula and cell parameters is 4.61 g/cm³. ## Colors and Varieties This mineral has a characteristic orange-brown to reddish-brown color. No color varieties or commercial forms are known. ## History and Name Barwoodite was discovered in nepheline syenite at the Poudrette quarry on Mont Saint-Hilaire in Quebec, Canada. It was described and approved as a new mineral species by the International Mineralogical Association (IMA) in 2010 (IMA2010-015). The name honors Charles F. Barwood (b. 1934), an American geologist and mineralogist, for his contributions to mineralogy research, including the discovery of several new minerals.

Properties

Mohs hardness: 5
Luster: Vitreous
Streak: Pale brown
Density: 4.61
Cleavage: Perfect on {0001}
Fracture: Uneven
Transparency: Translucent
Crystal system: Trigonal

Diagnostic features

## Identification Identification of barwoodite is impossible without specialized equipment. It requires chemical analysis (e.g., using an electron microprobe) to confirm the presence of manganese and niobium, and structural analysis (X-ray diffraction) to determine its unique crystal structure. Visually, under high magnification, orange-brown, tabular crystals with a vitreous luster can be observed. ## Differentiation from Similar Minerals Visually, it can be confused with other microscopic, brown minerals occurring in the same environment, such as eudialyte, wöhlerite, or astrophyllite. Definitive differentiation is only possible based on chemical and crystallographic analysis. ## Crystal Forms Barwoodite forms very small, thin, tabular crystals with a lath-like cross-section, exhibiting a hexagonal outline. These crystals often group into radial aggregates or haphazard clusters on the surface of other minerals.

Geological environment

## Genesis Barwoodite is a mineral of magmatic origin. It forms in the late stages of crystallization within pegmatites and xenoliths associated with alkaline intrusions, such as nepheline syenites. It crystallizes under conditions of low silica activity and high concentration of rare elements, including niobium. ## Mineral Associations This mineral occurs in association with other rare minerals typical of nepheline syenites from Mont Saint-Hilaire. It most commonly co-occurs with aegirine, albite, microcline, nepheline, sodalite, eudialyte, catapleiite, sérandite, and wöhlerite. ## Localities The only confirmed locality for barwoodite in the world is its type locality – the Poudrette quarry on Mont Saint-Hilaire, La Vallée-du-Richelieu Regional County Municipality, Montérégie region, Quebec, Canada.

Rarity

Extremely rare

For collectors

## Quality Criteria As a microscopic mineral, the collector's value of a barwoodite specimen primarily depends on the abundance and quality of crystals visible under magnification. Specimens with clearly formed, sharp crystals creating aesthetic, radial aggregates are most prized. The contrast with the rock matrix and the presence of well-identified associated minerals confirming the paragenesis are also important. ## Popular Localities The only source of barwoodite specimens is the Poudrette quarry on Mont Saint-Hilaire in Canada. This locality is world-renowned for the occurrence of hundreds of rare and unique minerals, and specimens from there are highly valued by collectors specializing in microscopic minerals (so-called micromounts).

Care and storage

## Cleaning Due to the extreme rarity and microscopic size of crystals embedded in the host rock, barwoodite specimens should not be subjected to any mechanical or chemical cleaning methods. Any attempt at intervention risks irreversible damage to the delicate crystals. ## What to Avoid Contact with any chemicals, acids, or ultrasonic cleaning should be avoided. Specimens must not be heated or exposed to sudden temperature changes. They should be protected from dust and moisture. ## Storage Specimens containing barwoodite are best stored under stable conditions, in sealed, padded "micromount" boxes, which protect them from mechanical damage, dust, and humidity changes. Display should be away from direct sunlight and heat sources.

Sources

IMA Mineral List (CNMNC)