Barrerite

Chemical formula: Na<sub>2</sub>(Al<sub>2</sub>Si<sub>7</sub>)O<sub>18</sub>·6H<sub>2</sub>O

Barrerite is a rare mineral from the zeolite group, forming colorless or white, tabular crystals, often gathered in fan-shaped aggregates.

## Characteristics Barrerite is a hydrated sodium aluminosilicate, belonging to the zeolite group. It is the sodium analogue of stellerite. It forms characteristic, thin or thick tabular crystals, which often combine into fan-shaped, radial, or sheaf-like aggregates. It is usually colorless or white, less often taking on pinkish or yellowish hues, which is associated with the presence of impurities. ## Physical Properties This mineral is characterized by a hardness in the range of 3-4 on the Mohs scale. It has a vitreous luster, which becomes pearly on perfect cleavage planes. It is transparent to translucent. Its density is approximately 2.13 g/cm³. It exhibits perfect cleavage in one direction. ## Colors and Varieties White and colorless are dominant. Specimens can also be slightly tinted pink or yellow. No named color varieties or commercial varieties are distinguished. ## History and Name The name barrerite, given in 1974 by Ermanno Passaglia and D. Pongiluppi, honors Richard Maling Barrer (1910–1996), a New Zealand chemist who was a pioneer in the field of zeolite chemistry and synthesis. The mineral was first described based on specimens found in Capo Pula, in the province of Cagliari, Sardinia (Italy). ## Applications Due to its rarity, barrerite has no industrial applications and is solely an object of interest for mineral collectors.

Properties

Mohs hardness
3-4
Luster
Vitreous, Pearly on cleavages
Streak
White
Density
2.13
Cleavage
Perfect on {010}
Fracture
Uneven to Conchoidal
Transparency
Transparent to Translucent
Crystal system
Orthorhombic

Diagnostic features

## Identification Characteristic features of barrerite include its tabular crystal habit, tendency to form fan-shaped and sheaf-like aggregates, perfect cleavage in one direction, and pearly luster on its cleavage planes. Its occurrence in gas vesicles in volcanic rocks is also an important clue. ## Distinguishing from Similar Minerals Barrerite is visually almost identical to stellerite and stilbite. A definitive distinction between these minerals is almost exclusively possible through chemical analysis (barrerite is a sodium mineral, while stellerite and stilbite are dominated by calcium). It differs from heulandite in crystal habit and cleavage direction. ## Crystal Forms Crystals are tabular, flattened along one of the axes. They most often occur in the form of radial or fan-shaped aggregates, as well as aggregates resembling sheaves or bow ties.

Geological environment

## Genesis Barrerite is a hydrothermal mineral. It forms at low temperatures, crystallizing in gas vesicles and fractures within altered volcanic rocks, such as andesites and rhyolites. ## Mineral Associations It often co-occurs with other minerals from the zeolite group, especially heulandite, mordenite, and laumontite. It is also accompanied by calcite and various varieties of quartz. ## Localities The most important and typical locality is Capo Pula in Sardinia, Italy. Significant specimens also come from Kuiu Island, Alaska (USA). This mineral has also been found in Teigarhorn, Iceland, and in several localities in Japan.

Rarity

Rare

For collectors

## Quality Criteria The most highly valued specimens are those with large, well-formed, and undamaged crystals, forming aesthetic, fan-shaped aggregates on a contrasting rock matrix. Transparency and lack of coloration also increase collector value. Completeness and lack of damage to delicate aggregates are important. ## Popular Localities Specimens from the type locality in Sardinia (Italy) and from Kuiu Island, Alaska (USA) are the most well-known and valued by collectors. They are considered classics for this species.

Care and storage

## Cleaning Barrerite specimens should be cleaned very carefully, using a soft brush and distilled water. Ultrasonic cleaners should be avoided, as they can cause cracking or complete destruction of delicate crystals. ## What to Avoid The mineral is sensitive to high temperatures, which can lead to dehydration and irreversible changes in its structure. Contact with acids should be avoided. Prolonged soaking in water is not recommended. It should be protected from direct sunlight. ## Storage Collector's specimens of barrerite, due to their low hardness and perfect cleavage, should be stored in separate boxes or display cases, away from harder minerals. Stable conditions should be ensured, protecting them from dust and mechanical damage.

External references

Sources

Read more