Gortdrumite

Chemical formula: Cu₂₄Fe₂Hg₉S₂₃

Gortdrumite is a very rare copper, iron, and mercury sulfide, forming tiny, metallic grains in carbonate veins.

## Characteristics Gortdrumite is an extremely rare sulfide mineral, characterized by a complex chemical composition containing copper, iron, and mercury. It occurs as very fine, irregular grains, usually not exceeding 0.2 mm in size. These grains are embedded in the host rock, most commonly in calcite. Due to its microscopic size, it does not form crystals visible to the naked eye or specimens of significant size. In polished section under a reflected light microscope, it has a creamy-white color with a slight pinkish tint. ## Physical Properties As an opaque mineral with a metallic luster, gortdrumite is too small to determine its hardness, density, or other physical properties in a traditional manner. These data have not been measured and are based only on estimates derived from its composition and comparisons with similar minerals. It does not exhibit cleavage, and its fracture is uneven. ## Colors and Varieties The mineral has a uniform, creamy-white color with a pinkish tint, visible under the microscope. No color varieties or commercial forms are known. ## History and Name Gortdrumite was discovered in the Gortdrum copper mine in County Tipperary, Ireland. It was described and recognized as a new mineral species by the International Mineralogical Association (IMA) in 1984. Its name comes directly from the type locality (Gortdrum mine) where it was first identified.

Properties

Mohs hardness
3.5-4
Color
Blackish lead-gray
Luster
Metallic
Density
0
Cleavage
None
Fracture
Uneven
Transparency
Opaque
Crystal system
Triclinic

Diagnostic features

## Identification Identification of gortdrumite is only possible using advanced laboratory techniques, such as ore microscopy (in reflected light) and chemical analysis using an electron microprobe (EDS/WDS). In reflected light, it exhibits weak anisotropy. It is impossible to identify with the naked eye. ## Distinguishing from Similar Minerals Under the microscope, it can be confused with other fine, creamy sulfides, such as chalcopyrite, bornite, or tetrahedrite, with which it often coexists. Certain differentiation requires chemical composition analysis, which will show the presence of mercury – a key component of gortdrumite. ## Crystal Forms Gortdrumite occurs exclusively as anhedral (irregular), rounded grains and aggregates of microscopic size, dispersed within a calcite matrix.

Geological environment

## Genesis Gortdrumite forms as a result of low-temperature hydrothermal processes. At the type locality, it was found in calcite veins cutting sandstones mineralized with copper sulfides. ## Mineral Associations This mineral coexists with other sulfides, such as chalcopyrite, bornite, digenite, chalcocite, tennantite, as well as native mercury and cinnabar. The main associated mineral is calcite. ## Localities The only confirmed and described occurrence of gortdrumite in the world is its type locality – the Gortdrum mine in County Tipperary, southern Ireland. It is an endemic mineral to this single site.

Rarity

Extremely rare

For collectors

## Quality Criteria As a microscopic mineral, gortdrumite is not an object of collector trade in the form of isolated specimens. The only value for specialized collections (so-called "micromounts" or systematic collections) is possessing a rock fragment from the type locality where the presence of this mineral has been confirmed. The value of such a specimen is purely scientific and referential, not aesthetic.

Care and storage

## Cleaning Due to its microscopic nature and occurrence as inclusions in the host rock, individual gortdrumite grains are not subject to cleaning. Rock specimens containing gortdrumite can be mechanically cleaned using a soft brush to remove dust. ## What to Avoid Avoid contact with acids and strong chemicals that could react with sulfides and carbonate rock. As a mercury-containing mineral, heating should be avoided, as this could lead to the release of toxic fumes. ## Storage Specimens containing gortdrumite should be stored in stable conditions, away from moisture and chemical contaminants, in a dry place. Standard collector boxes or display cases are entirely sufficient.

External references

Sources

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