Sudoite

Chemical formula: Mg<sub>2</sub>Al<sub>3</sub>(Si<sub>3</sub>Al)O<sub>10</sub>(OH)<sub>8</sub>

Sudoite is a mineral from the chlorite group, forming microscopic, scaly crystals of white or greenish color, found in metamorphic rocks.

## Characteristics Sudoite is a mineral from the chlorite group, belonging to the layered silicates. It usually occurs as very fine, scaly or fibrous aggregates, rarely forming distinct, pseudohexagonal crystals of small size. Most often, it is found in the form of compact, earthy, or flaky masses. Due to the microscopic size of its crystals, its macroscopic features are difficult to observe, and identification requires advanced research methods. ## Physical Properties This mineral is very soft; its Mohs hardness ranges from 2.5 to 3.5. Sudoite lamellae are flexible but inelastic. It has a pearly, vitreous, or dull luster, depending on its form of occurrence. It is transparent to translucent. Its density is approximately 2.66 g/cm³. ## Colors and Varieties Sudoite is usually colorless, white, pale gray, or pale green. No named color varieties or commercial varieties are distinguished. ## History and Name The mineral's name honors the Japanese mineralogist and petrologist, Professor Toshio Sudo (1911–2000) from the University of Tokyo, in recognition of his contributions to the study of clay minerals. The mineral was described and approved as a new species in 1966. ## Applications Sudoite has no industrial applications. Its significance is purely scientific and collectible, although it rarely constitutes a primary object of interest due to its inconspicuous appearance and microscopic crystal sizes.

Properties

Mohs hardness
2.5-3.5
Luster
Pearly
Streak
White
Density
2.66
Cleavage
Perfect on {001}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Macroscopic identification of sudoite is practically impossible. Identification requires specialized methods, such as X-ray diffraction (XRD) or electron microprobe analysis (EMPA). In collections, it occurs as a component of rocks, often in association with other minerals that may suggest its presence. ## Distinguishing from Similar Minerals It can be confused with other minerals from the chlorite group (e.g., clinochlore), talc, muscovite, or kaolinite. All these minerals form similar, fine-grained, scaly, and soft aggregates. Definitive differentiation is possible only through laboratory analysis. ## Crystal Forms Sudoite forms microscopic, pseudohexagonal, tabular crystals. It usually occurs as very fine-grained, scaly, fibrous, or spherulitic aggregates. Masses can be compact or earthy.

Geological environment

## Genesis Sudoite is a low- to medium-temperature hydrothermal mineral and a product of low-grade metamorphism. It forms in altered volcanic rocks, in crystalline schists (especially in the greenschist facies), and in alteration zones around metal ore deposits. It can also form during diagenetic processes in sedimentary rocks. ## Mineral Associations It often co-occurs with minerals such as quartz, hematite, pyrophyllite, diaspore, other chlorites, illite, titanite, rutile, and minerals from the epidote group. ## Localities Important sudoite localities worldwide include the Rosebery deposit in Tasmania (Australia); the Uchinotai mine in Akita Prefecture (Japan); the vicinity of Dobšiná in Slovakia; the Březina region in the Czech Republic; the Kidd Creek mine in Ontario (Canada); as well as numerous occurrences in Switzerland, Austria, France, and the United States (e.g., in Michigan and North Carolina).

Rarity

Rare

For collectors

## Quality Criteria Sudoite specimens are rarely of interest to collectors due to their unimpressive appearance and microscopic size. Collectible value may only be attributed to samples from the type locality (locus typicus) or specimens where sudoite forms well-defined, though still small, aggregates in association with other, more attractive minerals. Precise documentation and analytical confirmation of the mineral's identity are crucial here. ## Popular Localities For collectors specializing in rare or systematic minerals, specimens from Japan (Uchinotai mine) and Tasmania (Rosebery), from which well-studied samples originate, will be the most sought after.

Care and storage

## Cleaning Sudoite specimens are very delicate and soft. They should be cleaned only carefully, using compressed air to remove dust. Contact with water is not recommended, as it can penetrate the aggregate structure and damage it. ## What to Avoid Avoid ultrasonic cleaners, all chemical agents, acids, and detergents. The mineral is susceptible to scratching and abrasion. It should be protected from high temperatures and humidity. ## Storage Specimens containing sudoite are best stored in closed, dry containers or display cases, away from dust and direct sunlight. Due to its softness, it should be kept separate from harder minerals to prevent scratching.

External references

Sources

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