Jordisite

Chemical formula: Mo₄+S₂-₂

Jordisite is an amorphous molybdenum sulfide, the non-crystalline equivalent of molybdenite, occurring as earthy, black coatings.

## Characteristics Jordisite is a molybdenum(IV) sulfide and represents its amorphous (non-crystalline) form. Unlike its crystalline counterpart, molybdenite, it does not form well-developed crystals. It most commonly occurs as earthy, powdery, or sooty aggregates, coatings, and crusts of a black color. Its appearance is dull and inconspicuous, often resembling graphite or pyrolusite. ## Physical Properties Due to its amorphous nature and occurrence in the form of soft aggregates, precise determination of hardness is difficult; it ranges from 1 to 2 on the Mohs scale. The mineral is very soft and soils fingers when touched. The luster is dull or earthy. It is opaque. The density ranges from 4.3 to 4.9 g/cm³. ## Colors and Varieties Jordisite is uniformly black. No color or commercial varieties are distinguished. Differences in appearance primarily result from the texture of the aggregates – from fine-grained and powdery to more compact, earthy masses. ## History and Name The mineral's name comes from Louis Jordis, a German chemist who first synthesized colloidal molybdenum sulfide. Jordisite was described as a mineral in 1909. ## Uses Jordisite, like molybdenite, is an ore of molybdenum, but due to its rarer occurrence in large concentrations, it has less economic significance. It is an object of interest for collectors specializing in rare minerals or ore minerals.

Properties

Mohs hardness: 1-2
Luster: Dull
Streak: Black
Density: 4.3-4.9
Fracture: Earthy
Transparency: Opaque

Diagnostic features

## Identification Jordisite is recognized by its characteristic sooty or earthy form, black color, and extreme softness (stains hands). Its dull, lusterless appearance is also a characteristic feature. Occurrence in association with uranium minerals or in the oxidation zones of sulfide deposits can be an additional clue. ## Distinguishing from Similar Minerals Jordisite can be confused with graphite, pyrolusite, or other black, earthy manganese oxides ("psilomelane"). It differs from graphite by a slightly different texture and the absence of the characteristic, slightly metallic luster. It can be difficult to distinguish from manganese oxides without chemical analysis, although manganese oxides are usually harder and denser. Unlike crystalline molybdenite, jordisite does not exhibit cleavage or metallic luster. ## Crystal Forms As an amorphous substance, jordisite does not form crystals. It occurs exclusively as earthy, powdery, sooty aggregates, as well as thin coatings and crusts.

Geological environment

## Genesis Jordisite is a low-temperature mineral. It forms under reducing conditions, often as a result of precipitation from aqueous solutions. It typically forms in organic-rich sediments, such as black shales. It is also found in reducing zones of uranium-vanadium deposits in sandstones ("roll-front" type) and as a weathering product of molybdenite in the oxidation zones of sulfide deposits. ## Mineral Associations This mineral often co-occurs with uraninite, coffinite, pyrite, marcasite, ilsemannite (secondary molybdenum sulfate), gypsum, as well as with bituminous substances and organic matter. In "roll-front" type deposits, it is accompanied by a characteristic assemblage of ore minerals from the reducing zone. ## Localities Significant occurrences of jordisite are known from uranium deposits in sandstones on the Colorado Plateau in the USA (Utah, Colorado, Arizona, New Mexico). It is also found in Germany (Thuringia), the Czech Republic, and in Black Sea sediments.

Rarity

Not very common

For collectors

## Quality Criteria The collector's appeal of jordisite lies not in its aesthetics, but in its rarity and scientific significance. The most prized specimens are those where jordisite forms distinct, thick layers or occurs in rich association with other rare minerals, e.g., well-formed gypsum crystals or uranium minerals. Contrast with a light matrix enhances visual appeal. Due to its nature, purity and "form" are not typical evaluation criteria. ## Popular Localities The most classic and sought-after specimens by collectors come from uranium deposits in the Grants region of New Mexico and from Montrose County, Colorado, USA.

Care and storage

## Cleaning Jordisite specimens are extremely delicate and soft. Wet cleaning should be avoided, as water can dissolve or destroy earthy aggregates. The safest method is to very carefully remove dust with a soft brush or a stream of compressed air from a distance. ## What to Avoid Contact with water, chemicals, and ultrasound should be absolutely avoided. Specimens are sensitive to abrasion and pressure – even touching with a finger can leave a mark and remove part of the mineral. It should not be heated or exposed to sudden temperature changes. ## Storage It is recommended to store specimens in closed, padded collector's boxes to protect them from dust, vibrations, and mechanical damage. Avoid keeping it in direct contact with other, harder minerals.

Sources

IMA Mineral List (CNMNC)