Caswellsilverite

Chemical formula: NaCr³⁺S²⁻₂

Caswellsilverite is an extremely rare sodium chromium sulfide, found exclusively in meteorites.

## Characteristics Caswellsilverite is a mineral with a metallic luster, occurring as extremely small, elongated or platy crystals, usually not exceeding 15x150 micrometers in size. It is observed as inclusions in other minerals, mainly in daubréelite. Due to the microscopic size of the crystals, its visual characteristics are difficult to assess without specialized equipment. ## Physical Properties The mineral is characterized by a metallic luster and is opaque. Its hardness and density have not been precisely measured due to the small size of the samples; however, the density calculated based on the chemical formula and unit cell parameters is 3.42 g/cm³. It exhibits perfect cleavage in one direction. ## History and Name The mineral's name honors Caswell Silver (1916-1988), an American geologist, entrepreneur, and philanthropist, in recognition of his contributions to the University of New Mexico. It was first described in 1983 by A. Okada and K. Keil based on material from the Norton County meteorite.

Properties

Mohs hardness
2
Color
Yellowish-grey, Grey
Luster
Metallic
Density
0
Cleavage
Perfect on {0001}
Transparency
Opaque
Crystal system
Trigonal

Diagnostic features

## Identification Identification of caswellsilverite is possible only through advanced laboratory techniques, such as scanning electron microscopy (SEM) with chemical composition analysis (EDS) or electron probe microanalysis (EPMA). In reflected light, it has a grayish-white color with a slight bluish tint and exhibits strong anisotropy. ## Distinguishing from Similar Minerals It can be confused with other sulfides found in meteorites, such as troilite or daubréelite. Definitive differentiation requires chemical analysis to confirm the presence of sodium and chromium as main components. ## Crystal Forms It forms microscopic, elongated crystals with a platy or acicular habit, often grouped into irregular aggregates.

Geological environment

## Genesis Caswellsilverite is a mineral of extraterrestrial origin. It forms under specific conditions during the formation or metamorphism of certain types of meteorites, specifically aubrites. It crystallizes in a highly reduced, oxygen-poor environment. ## Mineral Associations It co-occurs with other minerals typical of meteorites, such as daubréelite (in which it often forms inclusions), enstatite, kamacite, niningerite, perryite, schreibersite, sphalerite, and troilite. ## Localities Its occurrence has been confirmed in only a few meteorites. The type locality is the Norton County meteorite (Kansas, USA). It has also been identified in the Bustee (India), Khor Temiki (Sudan), and Mayo Belwa (Nigeria) meteorites.

Rarity

Extremely rare

For collectors

## Quality Criteria From a collector's perspective, the value of a specimen does not depend on the quality of the caswellsilverite itself (which is invisible to the naked eye), but on the scientific and aesthetic value of the meteorite in which it is found. The most valuable are well-documented fragments with analytically confirmed presence of this mineral.

Care and storage

## Cleaning Due to its extreme rarity and microscopic nature of occurrence (as inclusions in meteorites), specimens are not cleaned in the traditional sense of the word. Any interventions should be left to specialized laboratories. ## What to Avoid Avoid all chemicals, ultrasonics, temperature changes, and moisture, which could damage both the mineral itself and the surrounding meteorite matrix. ## Storage Meteorite specimens containing caswellsilverite should be stored under stable museum conditions, in a dry environment, preferably in specialized containers that protect against contamination and mechanical damage.

External references

Sources

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