Orlandiite

Chemical formula: Pb²⁺₃Cl₄(Se⁴⁺O₃)·H₂O

Orlandite is a very rare, hydrated lead and chlorine selenite, forming colorless, silky aggregates of acicular crystals.

## Characteristics Orlandite is a hydrated lead and chlorine selenite. It occurs as aggregates of small, acicular or capillary crystals, which can form spherulitic aggregates. Individual crystals are elongated and flexible. It is usually colorless to white, with a vitreous or silky luster, giving it a delicate appearance. ## Physical Properties This mineral is characterized by a vitreous to silky luster and is translucent. Its hardness and density have not been precisely determined. It exhibits perfect cleavage in one direction. ## Colors and Varieties Orlandite is usually colorless or white. No colored or commercial varieties have been distinguished. ## History and Name The mineral was approved by the IMA in 1996. Its name honors the Italian mineralogist and curator of the Natural History Museum of the University of Pisa, Paolo Orlandi (born 1954), for his contributions to mineralogy, including the discovery of many new minerals. ## Uses Due to its extreme rarity, orlandite has no industrial applications and is solely an object of interest for collectors specializing in rare minerals or minerals from specific localities.

Properties

Luster
Vitreous to silky
Streak
White
Density
0
Cleavage
Perfect {010}
Transparency
Translucent
Crystal system
Triclinic

Diagnostic features

## Identification Orlandite can be identified by its characteristic form – it creates aggregates of very small, acicular or capillary crystals, often in the form of spherulites. Its silky luster, white color, and occurrence in paragenesis with other rare selenites and sulfates are key indicators. ## Distinguishing from Similar Minerals It can be confused with other rare, secondary lead minerals of similar appearance, such as anglesite or cerussite in acicular form. Definitive differentiation requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical analysis (EDS/WDS), due to the presence of selenium. ## Crystal Forms Crystals are acicular or capillary, elongated along the [100] axis and flattened. They usually form radial, spherulitic, or tangled aggregates.

Geological environment

## Genesis Orlandite is a secondary mineral, forming in the oxidation zones of polymetallic ore deposits. It forms as a result of the weathering of primary minerals containing selenium and lead, in a chloride-rich environment, likely originating from marine waters. ## Mineral Associations At the type locality, it co-occurs with anglesite, kermesite, lead anglesite, caledonite, and other as yet unnamed lead selenites. ## Localities The only confirmed occurrence of orlandite in the world is its type locality – the Baccu Locci mine in Villaputzu, in the province of South Sardinia, Italy.

Rarity

Extremely rare

For collectors

## Quality Criteria The most valued specimens are those with clearly formed, rich aggregates of acicular crystals, forming aesthetic spherulites or "nests" on a contrasting rock matrix. Association with other rare secondary minerals is also important. Due to the microscopic size of the crystals, specimens are primarily evaluated under magnification. ## Popular Localities The only source of orlandite specimens is the Baccu Locci mine in Italy, which makes every specimen from this locality extremely desirable for collectors specializing in "microminerals" and type locality specimens.

Care and storage

## Cleaning Orlandite specimens are extremely delicate and sensitive. Wet cleaning should be avoided. Any dust can be removed very carefully using a soft brush or a stream of compressed air from a distance. ## What to Avoid Avoid contact with water, chemicals, and sudden temperature changes. The crystals are brittle and flexible, but easily mechanically damaged. Do not expose it to direct sunlight. ## Storage It is recommended to store specimens in closed, stable containers (micromount type) to protect them from dust, humidity, and physical damage. Avoid vibrations and shocks.

External references

Sources

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