Ginelfite

Chemical formula: Ag¹⁺₂(Ag¹⁺₀.₅Fe²⁺₀.₅)Tl¹⁺Pb²⁺₂₃.₅(Sb³⁺,As³⁺)₃₃.₅S²⁻₇₆

Ginelfite is an extremely rare lead-silver-thallium sulfosalt of antimony-arsenic, occurring as microscopic inclusions in other minerals.

## Characteristics Ginelfite is a very rare mineral from the sulfosalt group, identified only in the form of microscopic, anhedral (not exhibiting its own crystallographic forms) grains, usually not exceeding 100 micrometers in size. It occurs as inclusions in other minerals, most often in lengenbachite. Due to its extremely small size, its visual characteristics, such as luster or color in mass, have not been fully characterized. In reflected light under a polarizing microscope, it exhibits a grayish-white color with a greenish tint. ## Physical Properties Due to its microscopic mode of occurrence, most physical properties of ginelfite have not been determined. Hardness is unknown, but it can be assumed that it is a relatively soft mineral, similar to other complex sulfosalts. The density calculated based on the chemical formula and unit cell parameters is 5.83 g/cm³. It is an opaque mineral. ## History and Name The mineral was approved by the International Mineralogical Association (IMA) in 2010 under number IMA2010-028. Its name honors Professor Günter E. Nelf (1919–2006) from the University of Heidelberg, in recognition of his contribution to research on complex sulfosalts from the Lengenbach quarry in Switzerland. It was described by a team of researchers led by Stefan Graeser.

Properties

Mohs hardness
3-3.5
Color
dark grey
Luster
Metallic
Streak
black
Density
5.765
Fracture
Conchoidal
Transparency
Opaque
Crystal system
Triclinic

Diagnostic features

## Identification Identification of ginelfite is possible only using advanced laboratory techniques. This requires analysis in reflected light on polished sections and chemical analysis using an electron microprobe (EDS/WDS) to confirm its complex chemical composition. Optical features in reflected light, such as weak anisotropy and lack of internal reflections, are helpful. ## Distinguishing from Similar Minerals Ginelfite occurs in paragenesis with many other visually very similar sulfosalts from Lengenbach. It can be confused with lengenbachite, sartorite, dufrénoysite, or baumhauerite. Certain differentiation from these minerals is possible only on the basis of precise chemical composition analysis, which for ginelfite is unique due to the simultaneous presence of silver, thallium, iron, lead, antimony, and arsenic in specific proportions. ## Crystal Forms This mineral does not form visible crystals. It occurs exclusively as anhedral, irregular grains intergrown with other minerals.

Geological environment

## Genesis Ginelfite forms as a result of hydrothermal processes in metamorphic deposits. Its only known locality, the Lengenbach quarry, is a deposit embedded in dolomitic marbles (the so-called Binnit dolomite), which underwent metamorphism under amphibolite facies conditions. Sulfosalt mineralization is the result of hydrothermal solutions rich in sulfur, arsenic, antimony, lead, thallium, and other metals. ## Mineral Associations Ginelfite occurs in close association with other sulfosalts. Most often, it is found as inclusions in lengenbachite. It also co-occurs with minerals such as sartorite, dufrénoysite, baumhauerite, hutchinsonite, hatchite, wallisite, tennantite-(Zn), and pyrite. ## Localities The only confirmed occurrence of ginelfite in the world (type locality) is the Lengenbach quarry in the Binn Valley (Binntal) in the canton of Valais, Switzerland. This is a classic locality for many rare sulfosalts.

Rarity

Extremely rare

For collectors

## Quality Criteria Ginelfite is a mineral of purely scientific and systematic significance; it does not form specimens in the common sense of the word. Collector value pertains to the entire host rock specimen (most often lengenbachite in dolomite) in which ginelfite has been identified. The value of such a specimen is determined by the abundance and quality of the crystals of the main mineral (e.g., lengenbachite) and the analytically confirmed presence of ginelfite. It is an object desired exclusively by specialized collectors of systematic minerals and micromounts. ## Popular Localities The only source of specimens with ginelfite is the Lengenbach quarry in Switzerland. These specimens are extremely difficult to acquire and appear on the market very rarely, usually originating from old collections or from prospectors specializing in this locality.

Care and storage

## Cleaning Due to its occurrence exclusively as microscopic inclusions within other rare and delicate minerals (mainly lengenbachite), host specimens containing ginelfite should not be subjected to any invasive cleaning methods. Any attempt at chemical or mechanical cleaning would destroy both the ginelfite and the host mineral. ## What to Avoid All chemicals, ultrasonics, temperature changes, and moisture should be avoided. Specimens from Lengenbach are susceptible to oxidation and degradation under inappropriate conditions. ## Storage Specimens containing ginelfite, being inherently rare and valuable scientific samples, must be stored under stable conditions. Storage in specialized, sealed collector boxes (so-called "micromount boxes") is recommended to protect against dust, light, and humidity fluctuations.

External references

Sources

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