Vaughanite

Chemical formula: Tl¹⁺Hg¹⁺Sb³⁺₄S²⁻₇

Vaughanite is an extremely rare, light gray thallium, mercury, and antimony sulfosalt, occurring as microscopic grains.

## Characteristics Vaughanite is a very rare mineral from the sulfosalt group, composed of thallium, mercury, antimony, and sulfur. It forms anhedral (irregular), microscopic grains, usually not exceeding 100 micrometers in size. It occurs as inclusions in other minerals, most often in barite. Due to its size, its visual features are only discernible under high magnification. ## Physical Properties This mineral is characterized by a hardness ranging from 3-3.5 on the Mohs scale. It is opaque and has a metallic luster. Its density has not been precisely determined. ## Colors and Varieties Under a microscope in reflected light, vaughanite is light gray. No varieties of it are distinguished. ## History and Name The mineral is named in honor of David J. Vaughan (born 1946), a professor of mineralogy at the University of Manchester, England, for his contributions to the study of sulfides and sulfosalts. It was discovered and described in 1987 by W.H. Paar, D.C. Harris, and A.C. Roberts based on samples from the Hemlo gold deposit in Canada.

Properties

Mohs hardness
3-3.5
Luster
Metallic
Streak
Black
Density
0
Transparency
Opaque
Crystal system
Triclinic

Diagnostic features

## Identification Identification of vaughanite is only possible using advanced laboratory techniques, such as electron microprobe analysis (EDS/WDS) and X-ray diffraction (XRD). Its optical properties in reflected light, such as its light gray color and weak anisotropy, are helpful but insufficient for unambiguous identification. ## Distinguishing from Similar Minerals It can be confused with other microscopic, gray sulfosalts found in similar environments, such as parapierrotite, pierrotite, or other lead and antimony sulfosalts. Definitive differentiation requires chemical composition analysis. ## Crystal Forms Vaughanite forms only very small, irregular, anhedral grains, often occurring as inclusions in other minerals.

Geological environment

## Genesis Vaughanite forms as a result of hydrothermal processes in gold deposits. In its type locality (Hemlo), it is associated with a late stage of mineralization, crystallizing at low temperatures in barite veins cutting the gold ore. ## Mineral Associations This mineral coexists with barite, criddleite, cinnabar, realgar, stibnite, parapierrotite, and other thallium sulfosalts. ## Localities The only confirmed and described occurrence of vaughanite in the world is its type locality - the Golden Giant mine within the Hemlo gold deposit, in the Thunder Bay District, Ontario, Canada.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of a vaughanite specimen is assessed solely based on its scientific value and locality. Since the mineral is microscopic, the value of a sample is determined by the richness of the mineral association and confirmation of vaughanite's presence through analysis. It has no aesthetic significance. ## Popular Localities The only source of specimens is the Golden Giant mine in Canada. Material from this locality is extremely difficult to acquire and is found almost exclusively in institutional and specialized collections.

Care and storage

## Cleaning Due to its microscopic size and occurrence as inclusions, individual vaughanite specimens are not cleaned. Cleaning of the host rock should be kept to an absolute minimum, preferably using compressed air to remove dust. ## What to Avoid All chemical and mechanical cleaning methods (e.g., ultrasonics) that could damage both the mineral itself and its surrounding matrix should be avoided. As a mineral containing thallium and mercury, it is toxic, and direct contact and inhalation of dust should be avoided. ## Storage Specimens containing vaughanite should be stored under stable conditions, in sealed containers or display cases, away from moisture and contaminants. The sample must be clearly labeled due to the mineral's toxicity.

External references

Sources

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