Marathonite

Chemical formula: Pd<sub>₂₅</sub>Ge<sub>₉</sub>

Marathonite is an extremely rare palladium germanide, found exclusively as microscopic grains in copper and platinum-group element deposits.

## Characteristics Marathonite is a palladium germanide with a complex chemical formula. It occurs as anhedral (irregular), rounded grains not exceeding 100 micrometers in size. It is typically intergrown with other platinum-group minerals (PGM). In reflected light under a microscope, its color is grayish-white. ## Physical Properties Its Mohs hardness is estimated at 5. The mineral is completely opaque and exhibits a strong, metallic luster. Its density, calculated based on chemical composition and unit cell parameters, is very high at 11.96 g/cm³. ## Colors and Varieties No color varieties or commercial forms are distinguished. The mineral has a consistent, grayish-white color in reflected light. ## History and Name The mineral's name comes from the Marathon deposit in Ontario, Canada, which is its type locality. It was officially approved as a new mineral species by the International Mineralogical Association (IMA) in 2009. ## Applications Due to its extreme rarity and microscopic size, marathonite has no industrial applications. Its significance is purely scientific, and for collectors, it is an object of interest only in specialized collections of microscopic minerals.

Properties

Mohs hardness: 5
Luster: Metallic
Density: 11.96
Cleavage: None
Transparency: Opaque
Crystal system: Cubic

Diagnostic features

## Identification Identification of marathonite is possible only through advanced laboratory techniques, such as chemical composition analysis using an electron microprobe (EDS/WDS) and crystallographic analysis by X-ray diffraction (XRD). In reflected light under a microscope, it is grayish-white and has a strong metallic luster. ## Distinguishing from Similar Minerals It can be confused with other visually similar platinum-group minerals, such as keithconnite, palladogermanide, or wasilite, with which it often co-occurs. Definitive differentiation is only possible based on precise chemical analysis. ## Crystal Forms Marathonite forms exclusively anhedral (irregular), rounded grains, often as small inclusions in other minerals or in intergrowths with other platinum-group elements. Naturally formed crystal faces have not been observed.

Geological environment

## Genesis Marathonite forms in the late stages of gabbroic magma crystallization, within copper and platinum-group element (PGE) deposits. It is a magmatic mineral, crystallizing from residual melts rich in palladium and germanium. ## Mineral Associations It co-occurs with bornite, chalcopyrite, pentlandite, magnetite, and other rare PGE minerals such as keithconnite, palladogermanide, and wasilite. ## Localities The only confirmed occurrence worldwide is its type locality – the Marathon deposit, near the town of Marathon in the Thunder Bay District, Ontario, Canada.

Rarity

Extremely rare

For collectors

## Quality Criteria The collector's value of marathonite is purely scientific and sentimental. The attractiveness of a specimen is determined by the abundance of mineral grains in the rock matrix, their size (though always microscopic), and most importantly, confirmation of identification through instrumental analysis. ## Market Prices No data on market prices. The mineral is not subject to commercial trade due to its extreme rarity and microscopic nature. ## Popular Localities The only source of specimens is the type locality in Canada. Any specimen from this location containing confirmed marathonite is a valuable acquisition for specialized institutions and collectors.

Care and storage

## Cleaning Specimens containing marathonite, which are typically polished sections or microscopic preparations, are not cleaned in the traditional way. Any contact with chemicals and abrasive materials should be avoided. ## What to Avoid Specimens should be protected from scratching, impacts, and contact with acids and other aggressive chemical substances. Temperature and humidity changes do not significantly affect properly stored specimens. ## Storage Marathonite specimens should be stored in specialized micromount boxes or as protected microscopic preparations to shield them from mechanical damage and dust.

Sources

IMA Mineral List (CNMNC)