Thorneite

Chemical formula: Pb<sup>2+</sup><sub>6</sub>(Te<sup>6+</sup><sub>2</sub>O<sub>10</sub>)(CO<sub>3</sub>)Cl<sub>2</sub>(H<sub>2</sub>O)

Thorneite is a rare mineral from the tellurate, carbonate, and halide groups, forming colorless to white, platy crystals, discovered in the Grand Central Mine in Arizona.

## Characteristics Thorneite is a complex lead tellurate, carbonate, and chloride. It occurs as very small, platy or bladed crystals, usually not exceeding 0.2 mm in length. The crystals are colorless to white and form rosette-like or randomly oriented aggregates on the surface of the host rock. Due to the small size of the crystals, its visual features are difficult to observe without magnification. ## Physical Properties Thorneite crystals exhibit a luster described as vitreous to pearly. They are transparent to translucent. The hardness of the mineral has not been precisely determined, but it is soft and brittle. The density calculated based on the chemical formula and unit cell parameters is 6.49 g/cm³. ## Colors and Varieties This mineral is colorless to white. No color or commercial varieties have been distinguished. ## History and Name Thorneite was first described in 2012 by Anthony R. Kampf, Stuart J. Mills, Robert M. Housley, Joel Brugger, and John W. Anthony. The mineral is named in honor of Brent Thorne (born 1949), an American micromineral collector from Prescott, Arizona, who collected and first drew attention to the material in which the new mineral was identified. It was approved by the International Mineralogical Association (IMA) under number IMA2010-031. The type specimen is preserved in the collections of the Natural History Museum of Los Angeles County. ## Uses Thorneite has no industrial application. It is solely an object of interest for collectors specializing in rare minerals and microminerals, and also holds scientific significance.

Properties

Luster
Vitreous to pearly
Streak
White
Density
6.49
Cleavage
Perfect on {001}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Amateur identification of thorneite is practically impossible. Identification requires advanced analytical methods, such as X-ray diffraction (XRD) and chemical analysis (EDS/WDS). In a collection, it can be recognized based on the label and comparison with photographs of specimens from the type locality. Its characteristic habit is very small, colorless, platy crystals in rosette-like aggregates. ## Distinguishing from Similar Minerals At first glance, it can be confused with many other secondary lead minerals of white color and small crystals, such as cerussite, hydrocerussite, or other rare tellurates and sulfates. Definitive differentiation is only possible based on chemical and crystallographic analysis, which will show the simultaneous presence of lead, tellurium, a carbonate group, and chlorine. ## Crystal Forms Thorneite crystallizes as thin, platy crystals with a hexagonal or pseudohexagonal outline. These crystals often combine into rosette-like or radial aggregates, and also occur as randomly oriented clusters on the rock surface.

Geological environment

## Genesis Thorneite is a secondary mineral formed in the oxidation (weathering) zones of tellurium-rich ore deposits. At the type locality (Grand Central Mine), it formed as a result of the oxidation of primary tellurides in the presence of lead minerals and solutions containing carbonate and chloride ions. It forms in vugs and on fracture surfaces in the quartz host rock. ## Mineral Associations This mineral co-occurs with other rare, secondary tellurium and lead minerals. At the type locality, it has been found in association with minerals such as: backite, cerussite, chlorargyrite, dugganite, emmonsite, eztahlite, galena, goethite, hematite, hydrocerussite, quartz, schieffelinite, tellurite, and xocomecatlite. ## Localities The only confirmed occurrence of thorneite in the world is its type locality: the Grand Central Mine, located in the Tombstone Hills, Cochise County, Arizona, USA.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of a thorneite specimen is primarily assessed based on the richness and aesthetics of the crystal aggregates. Most valued are specimens with numerous, well-formed, rosette-like aggregates of colorless crystals, clearly contrasting with the host rock. Crystal size, although always small, is also important – larger and better-formed plates increase the specimen's value. Association with other rare tellurium minerals is also significant. ## Popular Localities The only source of collector specimens is the Grand Central Mine in Arizona, USA. This is a classic locality for many rare tellurates, making material from there particularly sought after by specialized collectors.

Care and storage

## Cleaning Thorneite specimens should be cleaned with the utmost care, exclusively using compressed air to remove dust. Due to its extreme rarity, small crystal size, and fragility, mechanical (brushes) or chemical methods are discouraged. ## What to Avoid Avoid contact with water, acids, and other chemicals that may damage or dissolve the delicate crystals. The mineral is brittle, so it should be protected from impacts, vibrations, and abrasion. It should not be heated or subjected to ultrasonic cleaning. ## Storage Thorneite specimens, typically microminerals, should be stored in specialized, sealed "micromount" boxes that protect them from dust, mechanical damage, and sudden changes in humidity. Avoid exposure to direct sunlight.

Sources

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