Wadalite

Chemical formula: Ca₆Al₅Si₂O₁₆Cl₃

Wadalite is a rare mineral of the sodalite group, forming small, spherical or spherulitic aggregates with a vitreous luster.

## Characteristics Wadalite is a mineral belonging to the sodalite group, characterized by a complex chemical composition. It typically occurs as small, spherical or spherulitic aggregates, less commonly forming small, isometric crystals in the shape of a rhombic dodecahedron. Its appearance is often inconspicuous, and macroscopic specimens are rare. ## Physical Properties Wadalite crystals exhibit a vitreous luster. The mineral is brittle, and its Mohs hardness is approximately 5.5, which makes it relatively hard but susceptible to scratching by common minerals such as quartz. Its density is close to 2.77 g/cm³. ## Colors and Varieties Wadalite is usually colorless, white, pale yellow, or light brown. No distinct color varieties or commercial forms have been described. ## History and Name The mineral was first described in 1987 by Tsutomu Fujita and Chiyoko Takeno. Its name comes from the Japanese mineralogist, Professor Tsunashiro Wada (1856-1920) of the University of Tokyo, in recognition of his contribution to the mineralogy of Japan. The type locality is the Fuka mine in Okayama Prefecture, Japan. ## Uses Due to its rarity and typically small crystal sizes, wadalite has no industrial applications. It is of scientific and collector's interest only.

Properties

Mohs hardness: 5.5
Luster: Vitreous
Streak: White
Density: 2.77
Cleavage: None
Fracture: Uneven
Transparency: Transparent to translucent
Crystal system: Cubic

Diagnostic features

## Identification Field identification of wadalite is practically impossible due to its appearance and small size. In a collection, it can be recognized by its characteristic spherical or spherulitic aggregate form and vitreous luster. Definitive identification requires advanced analytical methods such as X-ray diffraction (XRD) or chemical analysis (EDS/WDS). ## Distinguishing from Similar Minerals Wadalite can be confused with other minerals forming similar spherulitic aggregates, such as calcite, aragonite, or some zeolites. It is distinguished from them by its greater hardness (in the case of calcite) and the lack of reaction with hydrochloric acid characteristic of carbonates. It differs from zeolites in chemical composition and optical properties. ## Crystal Forms Wadalite most often forms spherical, radial aggregates (spherulites). Less commonly, single, well-formed crystals in the shape of a rhombic dodecahedron {110}, often with rounded faces, are found.

Geological environment

## Genesis Wadalite is a mineral formed during contact metamorphism (skarns). It forms as a result of reactions between carbonate rocks (limestones) and magmatic intrusions at relatively high temperatures. It is a typical mineral of contact zones rich in calcium and aluminum. ## Mineral Associations This mineral often co-occurs with other skarn minerals, such as gehlenite, larnite, spurrite, mayenite, wollastonite, grossular, and calcite. The presence of these minerals is an important clue in the search for and identification of wadalite. ## Localities The most important and well-documented wadalite localities worldwide include: - Japan: Fuka mine, Okayama Prefecture (type locality). - Germany: Eifel Mountains, including the Laacher See region, where it occurs in volcanic ejecta. - Israel: Negev Desert, in the Hatrurim Formation. - Russia: In some alkaline intrusions.

Rarity

Very rare

For collectors

## Quality Criteria For collectors, specimens with well-formed, visible-to-the-naked-eye crystals are most desirable, which is a great rarity. Rich spherulitic aggregates on a contrasting rock matrix are also highly valued. Purity and lack of mechanical damage significantly increase the value of a specimen. Due to its rarity, even microscopic but well-defined crystals are considered valuable. ## Popular Localities The most prized wadalite specimens, often considered the best in the world, come from localities in the Eifel Mountains in Germany. Specimens from the type locality in Japan primarily hold historical and scientific value.

Care and storage

## Cleaning Wadalite specimens should be cleaned very carefully, using a soft brush to remove dust. Due to possible reactivity with acids, no chemical cleaning agents should be used. If necessary, distilled water can be used, and the specimen should then be thoroughly dried. ## What to Avoid Avoid contact with acids, especially hydrochloric acid, which can damage the mineral. Do not subject it to sudden temperature changes or ultrasonic cleaners. Store away from moisture. ## Storage It is recommended to store wadalite specimens in a dry place, in separate, padded collector's boxes, to avoid scratching by harder minerals. It should be protected from dust and direct sunlight.

Sources

IMA Mineral List (CNMNC)