Finescreekite

Chemical formula: [Pb²⁺₄(OH)₄](S⁶⁺O₃S²⁻)₂

Finescreekite is a rare lead thiosulfate sulfate, distinguished by its white, platy crystals and perfect cleavage.

## Characteristics Finescreekite is a rare, complex lead sulfate containing a thiosulfate anion. It forms very small, thin, platy crystals, typically not exceeding 1 mm in size, which often occur in loose, rosette-like or irregular aggregates. The crystals are colorless to white and exhibit a pearly luster on cleavage surfaces. ## Physical Properties This mineral is very soft, with a Mohs hardness of approximately 2.5. It is relatively dense due to its high lead content (calculated density is 5.675 g/cm³). The crystals are flexible and pliable, which is an unusual characteristic. The luster is pearly to vitreous. ## Colors and Varieties Finescreekite occurs in uniform colors – it is colorless to white. No colored or commercial varieties are known. ## History and Name The mineral's name comes from Fines Creek, a stream that flows near its discovery site. Finescreekite was first identified in material from the Redmond Mine in Haywood County, North Carolina, USA. It was approved as a new mineral species by the International Mineralogical Association (IMA) in 2012. ## Uses Due to its extreme rarity and microscopic crystal sizes, finescreekite has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals or sulfate minerals.

Properties

Mohs hardness
2.5-0
Luster
Pearly
Streak
white
Density
5.675
Cleavage
excellent cleavage on {001}, fair on {100}, {010}, and {110}
Fracture
Step-Like
Transparency
Translucent
Crystal system
Orthorhombic

Diagnostic features

## Identification Finescreekite can be recognized by its characteristic form – it creates extremely thin, colorless to white, platy crystals with a pearly luster. Its occurrence in association with other rare lead sulfates in a specific geological environment is a key indicator. A white streak and very low hardness are also auxiliary features. ## Distinguishing from Similar Minerals It can be confused with other secondary lead minerals of similar appearance, such as anglesite or cerussite in platy form, as well as with lanarkite, with which it often co-occurs. However, finescreekite is distinguished by its unique chemical composition (presence of the thiosulfate group), crystal flexibility, and perfect cleavage in one direction. Final differentiation requires advanced analytical methods, such as X-ray diffraction (XRD). ## Crystal Forms Crystals are tabular or platy, very thin, with a hexagonal or irregular outline. They usually form loose, rosette-like aggregates or disordered clusters on the surface of the host rock.

Geological environment

## Genesis Finescreekite is a secondary mineral formed in the oxidation zones of ore deposits containing galena (lead sulfide). It forms as a result of the reaction of sulfate-rich solutions with primary sulfide minerals under low temperature and pressure conditions. ## Mineral Associations This mineral co-occurs with other secondary lead minerals. In its type locality, it was found in association with lanarkite, anglesite, pyromorphite, leadhillite, mattheddleite, susannite, and galena. ## Localities The only confirmed and described occurrence of finescreekite in the world is its type locality – the Redmond Mine, located near Waterville Lake in Haywood County, North Carolina, USA.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of finescreekite specimens is primarily assessed based on the richness and aesthetics of the crystal aggregates. Most valued are specimens with clearly formed, undamaged, rosette-like clusters of white crystals, contrasting with the darker host rock. Due to the microscopic nature of the mineral, the size of individual crystals is not a key criterion; rather, the overall abundance on the specimen is important. ## Popular Localities The only source of finescreekite specimens is its type locality in North Carolina, USA. All materials available on the collector's market originate from this single mine.

Care and storage

## Cleaning Specimens should be cleaned with utmost care, using only compressed air to remove dust. Due to the extreme delicacy and small size of the crystals, any mechanical contact, including with water or a soft brush, risks their destruction. ## What to Avoid Avoid contact with water, chemicals (especially acids), ultrasound, and sudden temperature changes. The crystals are very soft, flexible, and susceptible to mechanical damage. They should be protected from vibrations and shocks. ## Storage It is recommended to store specimens exclusively in sealed, padded "micromount" boxes to protect them from dust, moisture, and physical damage. Display should be in closed display cases, away from sources of vibration.

External references

Sources

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