Georgiadesite

Chemical formula: Pb²⁺₄(As³⁺O₃)Cl₄(OH)

Georgiadesite is a rare, secondary lead mineral, occurring as colorless to yellowish, tabular crystals with a strong, adamantine luster.

## Characteristics Georgiadesite is a rare lead arsenate with additional chloride and hydroxyl anions. It forms thin, tabular crystals, often with a hexagonal or pseudohexagonal outline, which can reach up to 2 mm in size. It also occurs as rosette-like or radial aggregates. It is a transparent to translucent mineral with a strong, almost adamantine luster. ## Physical Properties Georgiadesite is a relatively soft and very dense mineral, which is typical for lead minerals. Its Mohs hardness is approximately 3.5. Luster is one of its most characteristic features – described as strongly resinous to adamantine. The crystals are brittle and exhibit perfect cleavage in one direction. ## Colors and Varieties This mineral is typically colorless, white, pale yellow, or yellowish-green. No named varieties have been distinguished. ## History and Name Georgiadesite was first described in 1907 by the French mineralogist Alexandre Lacroix and the Greek chemist K. D. Zenginises. The mineral is named in honor of Mr. Georgiadès, director of the mine in Laurion, Greece, where the mineral was discovered. ## Uses Due to its extreme rarity, georgiadesite has no industrial applications. It is solely of interest to collectors of rare minerals and scientists.

Properties

Mohs hardness
3.5
Color
White, brownish yellow; colourless in transmitted light.
Luster
Adamantine to Resinous
Streak
White
Density
6.3
Cleavage
Perfect on {001}
Fracture
Uneven
Transparency
Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Key diagnostic features include a thin-tabular crystal habit, often with a pseudohexagonal outline, very high luster (resinous to adamantine), high density, and occurrence in the oxidation zones of lead deposits. It reacts with hydrochloric acid. ## Distinguishing from Similar Minerals It can be confused with other rare, secondary lead minerals with a tabular habit, such as fiedlerite or laurionite, which occur in the same environment. Final differentiation usually requires advanced analytical methods (XRD, EDS), although georgiadesite stands out due to its exceptionally strong luster. ## Crystal Forms Crystals are thin, tabular, flattened parallel to the cleavage plane. They often form radial or rosette-like aggregates, as well as thin crusts on the surface of the host rock.

Geological environment

## Genesis Georgiadesite is a secondary mineral forming in the oxidation zones (gossans) of polymetallic deposits rich in lead and arsenic. It forms as a result of the reaction of ore-bearing waters with ancient metallurgical slags that came into contact with salty seawater, which is characteristic of the Laurion locality. ## Mineral Associations It most commonly co-occurs with other secondary lead minerals, such as laurionite, fiedlerite, penfieldite, paralaurionite, anglesite, cerussite, as well as with calcite and limonite. ## Localities The most important and classic locality for georgiadesite is the Laurion district in Attica, Greece. This is its type locality, from which the best-known specimens originate. Outside of Greece, its presence has been reported in small quantities in mines on the coast of Cornwall, United Kingdom.

Rarity

Very rare

For collectors

## Quality Criteria The most prized specimens are those with well-formed, sharp crystals with a pseudohexagonal outline, forming aesthetic, rosette-like aggregates. A strong, adamantine luster and crystal transparency are highly valued. Crystal size and abundance on the rock matrix also significantly increase collector value. ## Popular Localities By far the most sought-after and valued specimens come from the historic type locality – the Laurion district in Greece. Specimens from other localities are extremely rare and are a great treat for specialized collectors.

Care and storage

## Cleaning Due to its fragility and rarity, mechanical cleaning is highly inadvisable. Only very careful removal of dust with a soft brush or a photographic air blower is permissible. Avoid contact with water and all chemicals. ## What to Avoid Avoid contact with acids and other chemicals that may damage the mineral. It is sensitive to shocks and impacts due to its brittleness and perfect cleavage. It should not be heated or cleaned with ultrasonics. ## Storage Georgiadesite specimens should be stored in separate, padded collector boxes to protect them from mechanical damage and dust. They should be protected from contact with harder minerals.

External references

Sources

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