Reyerite

Chemical formula: Na₂Ca₁₄Al₂Si₂₂O₅₈(OH)₈·₆H₂O

Reyerite is a hydrated layered sodium and calcium silicate, forming characteristic pearly aggregates in the form of rosettes and spherulites.

## Characteristics Reyerite is a mineral from the phyllosilicate group, chemically classified as a hydrated sodium and calcium silicate. Its most typical and recognizable forms are spherical aggregates (spherulites) and radial clusters resembling rosettes, composed of small, platy crystals. It also occurs in lamellar and scaly aggregates. A characteristic feature of reyerite is its distinct pearly luster on cleavage surfaces, which transitions to vitreous elsewhere. ## Physical Properties The hardness of reyerite on the Mohs scale ranges from 3 to 4, making it a relatively soft mineral. It has perfect cleavage in one direction, causing it to easily split into thin plates or scales. Its density ranges from 2.55-2.58 g/cm³. It is a transparent to translucent mineral. ## Colors and Varieties Reyerite is most often white or colorless. It can also take on yellowish-white or grayish hues. No named color varieties or commercial varieties are distinguished. ## History and Name The mineral was first described in 1891 by the German mineralogist Karl Hintze. The name "reyerite" was given in honor of Eduard Reyer (1849-1914), an Austrian geologist and professor of geology at the University of Vienna, known for his research on the dynamics of geological processes.

Properties

Mohs hardness: 3-4
Luster: Pearly to Vitreous
Streak: White
Density: 2.55-2.58
Cleavage: Perfect on {0001}
Fracture: Uneven
Transparency: Transparent to Translucent
Crystal system: Trigonal

Diagnostic features

## Identification The most important diagnostic features of reyerite are its characteristic forms of occurrence – spherulites and rosettes – combined with a pearly luster on the lamellar surfaces. Low hardness (3-4) and perfect unidirectional cleavage are also key. Occurrence in cavities of volcanic rocks (basalts) in association with zeolites is a strong indicator. ## Distinguishing from Similar Minerals Reyerite is sometimes confused with other white layered silicates. - **Gyrolite** forms similar spherulites, but often with a more distinct, spherical shape and can be harder. - **Truscottite** is visually almost identical and often co-occurs with reyerite; their definitive distinction requires advanced analytical methods (XRD). - **Talc** is much softer (hardness 1) and feels greasy to the touch. - **Apophyllite** has a different, tetragonal crystal form and a more distinct vitreous luster. ## Crystal Forms Reyerite crystallizes in the trigonal system. It rarely forms well-developed, hexagonal platy crystals. It usually occurs in the form of radial aggregates, rosettes, spherulites, and lamellar, scaly, or fibrous aggregates.

Geological environment

## Genesis Reyerite is a hydrothermal mineral, forming at low temperatures. It typically forms as an alteration product of volcanic rocks, filling gas vesicles (amygdules) and fractures in basalts and andesites. It is less commonly found in contact metamorphic zones (skarns) and manganese deposits. ## Mineral Associations This mineral often co-occurs with zeolites (including analcime, natrolite, scolecite, heulandite), as well as with apophyllite, gyrolite, tobermorite, prehnite, and calcite. ## Localities Key global localities for reyerite include vesicles in basalts in Greenland (e.g., Niakornat, the historical type locality) and on the Isle of Mull in Scotland. Significant specimens come from the Deccan Traps in India (around Pune and Mumbai), where it forms large, impressive rosettes. It also occurs in Iceland and the United States (e.g., on the Keweenaw Peninsula in Michigan and in California).

Rarity

Not very common

For collectors

## Quality Criteria The collector's value of reyerite primarily depends on the form and aesthetics of the specimen. Well-formed, sharp, and undamaged rosettes or complete spherulites with a distinct pearly luster are most highly prized. The attractiveness of a specimen is significantly enhanced by a contrasting rock matrix or association with other minerals, such as shiny apophyllite crystals or colorful zeolites. Large, isolated aggregates are rarer and more sought after. ## Popular Localities Specimens from India (Deccan region) are considered the best for collectors, renowned for their large, well-formed rosettes with excellent luster, often associated with other zeolite group minerals. Classic, though often less spectacular, specimens come from historical localities in Scotland and Greenland.

Care and storage

## Cleaning Reyerite specimens should be cleaned very carefully due to their softness and perfect cleavage. It is best to use a soft brush to remove dust. If necessary, it can be quickly rinsed in distilled water and immediately dried. Ultrasonic cleaners should be absolutely avoided, as they can cause delicate aggregates to disintegrate. ## What to Avoid The mineral is susceptible to mechanical damage – scratches and impacts. It should be protected from contact with harder minerals. As a hydrated mineral, it may be sensitive to prolonged exposure to high temperatures, which can lead to dehydration and dulling. Contact with acids and strong chemicals should be avoided. ## Storage Collector's specimens of reyerite are best stored in separate, padded boxes to prevent crushing and abrasion. It is not suitable for display in areas exposed to dust, vibrations, or direct sunlight.

Sources

IMA Mineral List (CNMNC)