Nakauriite

Chemical formula: Cu<sup>2+</sup><sub>8</sub>(S<sup>6+</sup>O<sub>4</sub>)<sub>4</sub>(CO<sub>3</sub>)(OH)<sub>6</sub>·48H<sub>2</sub>O

Nakaurite is a rare, hydrated copper sulfate and carbonate, forming delicate, fibrous aggregates of a light blue color.

## Characteristics Nakaurite is a secondary mineral from the sulfate group, chemically a hydrated copper sulfate, carbonate, and hydroxide. Its most characteristic feature is its occurrence in the form of extremely delicate, silky fibers that form radial aggregates, crusts, or small veins. Specimens typically have a light blue, sky blue, or blue-green color, somewhat resembling other secondary copper minerals. ## Physical Properties This mineral is extremely soft, with a Mohs hardness of only 1 to 2, meaning it can be scratched with a fingernail. It has a low density, approximately 2.03 g/cm³, and its luster is most often silky, sometimes transitioning to vitreous. It is translucent. Due to the enormous water content in its crystal structure (48 H₂O molecules), it is very unstable in dry environments. ## Colors and Varieties Nakaurite occurs in a uniform range of colors from light blue to sky blue and greenish-blue. No color or commercial varieties are distinguished. ## History and Name The mineral's name comes from its discovery locality – the Nakauri mine in Aichi Prefecture, Japan. It was first described in 1976 by Japanese mineralogists J. Suzuki and M. Ito. ## Uses Nakaurite has no industrial applications. It is solely an object of interest for collectors of rare minerals and scientists.

Properties

Mohs hardness
1-2
Luster
Silky to Vitreous
Streak
Light blue
Density
2.03
Cleavage
Perfect on {100}
Fracture
Fibrous
Transparency
Translucent
Crystal system
Orthorhombic

Diagnostic features

## Identification Nakaurite can be identified by its characteristic fibrous structure, silky luster, and light blue color. Key diagnostic features include its extreme softness (hardness 1-2) and instability in dry air. It often occurs as coatings and efflorescences on the walls of old mine workings. ## Distinguishing from Similar Minerals Nakaurite is sometimes confused with other secondary blue copper minerals: - **Aurichalcite**: Has a very similar appearance and color, but is slightly harder (2) and reacts vigorously with hydrochloric acid. Nakaurite, despite its carbonate content, reacts more weakly. - **Chalcanthite**: Is water-soluble, which is an easy test to distinguish it. It also usually forms more vitreous crystals or stalactites, rather than silky fibers. - **Serpierite**: Has a similar color, but forms aggregates of small, platy crystals and is more stable. ## Crystal Forms This mineral forms almost exclusively fibrous aggregates. The fibers can be chaotically arranged, form radial aggregates, or create silky-looking crusts and coatings.

Geological environment

## Genesis Nakaurite is a secondary mineral, formed in the oxidation zones of sulfide copper deposits. It is a typical "post-mining" mineral, meaning it forms contemporaneously as a result of mining activity. It forms as an efflorescence on the walls of mine tunnels and workings, crystallizing from sulfate-rich waters that seep through rocks containing copper minerals. ## Mineral Associations It often co-occurs with other secondary minerals, such as gypsum, brochantite, devilline, posnjakite, malachite, as well as primary minerals, e.g., chalcopyrite. ## Localities The most important occurrences of this rare mineral are the Nakauri mine in Japan (type locality), mines in the Lavrion area in Greece, as well as some mines in Arizona (USA), the Atacama Desert in Chile, and Cornwall (United Kingdom).

Rarity

Rare

For collectors

## Quality Criteria Nakaurite's collector appeal depends on the intensity of its blue color and the abundance and form of its fibrous aggregates. Specimens with well-developed, silky aggregates covering a significant area of the rock matrix are most valued. Association with other, color-contrasting minerals is also important. ## Popular Localities Specimens from Lavrion, Greece, are considered classic and most desirable, often characterized by beautiful color and well-formed aggregates. Material from the type locality in Japan is also prized by specialized collectors.

Care and storage

## Cleaning Nakaurite specimens are extremely sensitive to water and changes in humidity. Cleaning should only be done dry, using a very soft brush to remove dust or a gentle stream of compressed air from a distance. Any contact with water or other liquids is unacceptable. ## What to Avoid The greatest threat to nakaurite is dehydration (water loss). It is absolutely essential to avoid storing it in a dry environment, near heat sources (heaters, lamps), and in direct sunlight. Water loss causes the mineral to whiten, dull, and crumble into powder. It is also very brittle and sensitive to shocks. ## Storage The best storage method is to place the specimen in an airtight, sealed container (e.g., a "membrane box" or a sealed box) to maintain stable, elevated air humidity. Some collectors place a small piece of damp sponge in the container, taking care that it does not directly touch the mineral. Protect from vibrations and drops.

Sources

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