Riomarinaite

Chemical formula: Bi₃+S₆+O₄(OH)(H₂O)

Riomarinaite is a rare, hydrated bismuth sulfate, forming small, platy crystals with a pearly luster.

## Characteristics Riomarinaite is a very rare mineral from the sulfate group, chemically classified as a hydrated bismuth hydroxide sulfate. It occurs as very small, thin, platy crystals, which rarely exceed 0.2 mm. These crystals often form rosette-like or radial aggregates. Due to its small size, it is a mineral primarily accessible to specialized micromineral collectors. ## Physical Properties Riomarinaite crystals are flexible and pliable. The mineral is characterized by a pearly luster on cleavage surfaces and a vitreous luster on other faces. It is transparent to translucent. Its hardness and density have not been precisely determined due to its small size and rarity. ## Colors and Varieties Riomarinaite is colorless to white. No varieties have been distinguished. ## History and Name The mineral was discovered in the dumps of the Rio Marina iron ore mine on Elba Island, Italy. Its name, approved by the International Mineralogical Association (IMA) in 2013, comes directly from its type locality. It was described by a team of mineralogists, including Paolo Orlandi. ## Uses Riomarinaite has no industrial application. It holds only scientific and collector's significance as a very rare mineral.

Properties

Mohs hardness: 2-3
Color: light beige to light grey
Luster: Pearly
Streak: white to light grey
Density: 0
Cleavage: Perfect on {010}
Fracture: Irregular/Uneven
Transparency: Transparent to translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Identifying riomarinaite in practice is impossible without advanced analytical methods, such as Raman spectroscopy or X-ray diffraction (XRD), due to its small size and resemblance to other secondary sulfates. A preliminary characteristic may be its occurrence as small, colorless, pearly, platy crystals in paragenesis with other bismuth minerals. ## Distinguishing from Similar Minerals It can be confused with other microscopic sulfates, such as gypsum, alunogen, or other rare bismuth sulfates. Certain differentiation requires chemical and structural analysis. ## Crystal Forms Riomarinaite forms very thin, platy crystals with a hexagonal outline, often elongated. These crystals combine into small, rosette-like or radial aggregates.

Geological environment

## Genesis Riomarinaite is a secondary mineral, forming in the oxidation zones (gossans) of polymetallic deposits rich in bismuth. It forms as a result of the weathering of primary sulfides, mainly bismuthinite, in the presence of sulfate solutions. ## Mineral Associations At the type locality (Rio Marina, Elba), it co-occurs with bismuthinite, pyrite, quartz, hematite, goethite, and other rare bismuth sulfates, such as klebelsbergite and gunningite. ## Localities The only confirmed and described occurrence of riomarinaite in the world is its type locality – the Rio Marina mine on Elba Island, Tuscany, Italy.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of riomarinaite specimens is primarily assessed based on the richness and aesthetics of microcrystal aggregates on the rock matrix. Most valued are specimens with well-formed, distinct, rosette-like clusters of transparent crystals, contrasting with the substrate (e.g., hematite). The size of individual crystals, although always microscopic, also affects the value. ## Popular Localities The only source of collector specimens is the historic Rio Marina mine on Elba, Italy.

Care and storage

## Cleaning Specimens should only be cleaned with compressed air to remove dust. Due to the extreme delicacy and small size of the crystals, any mechanical contact, including with water or brushes, should be avoided. ## What to Avoid Avoid contact with all chemicals, ultrasonics, and sudden temperature changes. The crystals are very brittle and flexible, making them susceptible to mechanical damage. ## Storage Riomarinaite specimens should be stored exclusively in specialized micromineral boxes (so-called micromounts) to protect them from dust, shocks, and mechanical damage. Exposure to moisture should be avoided.

External references

https://www.mindat.org/min-27210.html