Henryite

Chemical formula: (Cu,Ag)<sub>3+x</sub>Te<sub>2</sub> (x~0.4)

Henryite is a rare copper-silver telluride, forming tiny, metallic grains in association with other tellurides.

## Characteristics Henryite is a very rare mineral from the telluride group. It occurs as anhedral (irregular) grains, usually not exceeding 200 micrometers in size. It is most often observed as inclusions in other minerals, especially in native gold or other tellurides. Its metallic appearance and rarity make it an object of interest mainly in scientific research. ## Physical Properties This mineral is characterized by a metallic luster and is opaque. Due to the microscopic size of its crystals, most physical properties, such as hardness or density, are difficult to measure precisely and are based on estimated or calculated data. ## Colors and Varieties Henryite has a color ranging from creamy white to pale yellow, often with a pinkish or purplish tint in reflected light. No varieties are distinguished. ## History and Name The mineral was first described in 1982 by A.J. Criddle, C.J. Stanley, and J.E. Chisholm. Its name honors Norman Fordyce McKerron Henry (1909–1983), a British mineralogist and professor at the University of Cambridge, who was a pioneer in ore microscopy and author of key works on the identification of opaque minerals in reflected light. ## Uses Henryite has no industrial or commercial significance. Its occurrence is solely of scientific and collecting interest, serving as an indicator of specific geochemical conditions in gold and tellurium deposits.

Properties

Mohs hardness
2.5
Luster
Metallic
Streak
Black
Density
8.55
Cleavage
None
Fracture
Uneven
Transparency
Opaque
Crystal system
Cubic

Diagnostic features

## Identification Identification of henryite is possible almost exclusively using advanced laboratory techniques. It requires analysis under a reflected light microscope (ore microscopy) and confirmation of chemical composition using an electron microprobe (EDS/WDS). Its characteristic creamy white color with a pinkish tint is an indication, but not a sufficient feature for certain identification. ## Distinguishing from Similar Minerals Henryite can be confused with many other tellurides of similar appearance, such as sylvanite, hessite, petzite, or kotschubeite. Differentiation is based on subtle differences in color, relative hardness (microhardness), and, most importantly, precise chemical composition analysis. ## Crystal Forms This mineral occurs exclusively as irregular, anhedral grains and aggregates. No well-formed crystals have been observed.

Geological environment

## Genesis Henryite is a mineral of hydrothermal origin. It forms in low-temperature solutions rich in tellurium and precious metals, which crystallize in quartz veins. It is a typical mineral for epithermal gold deposits. ## Mineral Associations It most often co-occurs with native gold, sylvanite, petzite, hessite, altaite, krennerite, as well as with pyrite and quartz. Its presence is strongly associated with other tellurides of gold, silver, and lead. ## Localities The most important and confirmed henryite localities worldwide include: - Emperor Mine in Vatukoula on Viti Levu island, Fiji (type locality). - Clogau St. David's Mine in Gwynedd, Wales, United Kingdom. - Gold deposit near Zhodino, Belarus.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of a specimen containing henryite is assessed solely through the prism of the host rock and associated minerals. Since henryite itself is microscopic, its collectible value depends on the richness and aesthetics of the entire mineral assemblage, e.g., visible occurrences of native gold or other, more spectacular tellurides. Specimens with analytically confirmed henryite, originating from the type locality (Fiji), are most valued in scientific collections. ## Popular Localities The most sought-after specimens come from the mineral's discovery site - the Emperor Mine in Fiji. Material from this locality has the greatest historical and scientific value.

Care and storage

## Cleaning Due to its microscopic nature and occurrence as inclusions in a rock matrix, individual henryite grains are not cleaned. The host specimen can be gently cleaned with compressed air or, if the surrounding rock allows, with a soft brush. ## What to Avoid Avoid contact with chemicals, especially acids, which can react with tellurides. Also, avoid ultrasonic cleaners and aggressive mechanical cleaning, which could damage the delicate matrix or the inclusions themselves. ## Storage Specimens containing henryite should be stored in stable conditions, away from moisture and chemical contaminants. It is best to keep them in closed collector boxes to prevent dust accumulation and potential chemical reactions with the atmosphere.

Sources

Read more