Junoite

Properties

Mohs hardness

3.5-4

Luster

Metallic

Streak

Black

Density

7.55

Cleavage

Perfect on {001}

Fracture

Uneven

Transparency

Opaque

Crystal system

Monoclinic

Diagnostic features

## Identification Junoite can be identified by its tin-white or steel-gray color, metallic luster, and characteristic acicular or bladed crystals, often forming radial aggregates. A black streak and high density are also important diagnostic features. It reacts with nitric acid. ## Distinguishing from Similar Minerals Junoite can be confused with other bismuth sulfosalts, such as aikinite, bismuthinite, or emplectite. Distinguishing it often requires advanced analytical methods, such as chemical analysis (EDS) or X-ray diffraction (XRD), due to subtle differences in appearance and physical properties. Co-occurrence with other bismuth minerals in a specific geological environment can be a clue. ## Crystal Forms Junoite crystals are monoclinic and have a prismatic, acicular, or bladed habit. They are elongated along one of the crystallographic axes. They typically occur as fibrous, radial, or tangled aggregates embedded in the host rock, less frequently as single, well-formed crystals.

Geological environment

## Genesis Junoite is a hydrothermal mineral. It forms in ore veins in contact metamorphic zones associated with igneous intrusions. It forms under medium to high-temperature conditions, in an environment rich in bismuth, lead, copper, sulfur, and selenium. ## Mineral Associations This mineral often co-occurs with other sulfides and sulfosalts. Its most common associations include: chalcopyrite, pyrite, covellite, bismuthinite, emplectite, aikinite, as well as native gold, magnetite, hematite, muscovite, and chlorite. At the type locality, it was found in association with pekoite and gladite. ## Localities The most important and type locality for junoite is the Juno mine in Tennant Creek, Northern Territory, Australia. Beyond Australia, its presence has been reported in several other locations worldwide, including the Băița Bihor mine in Romania, the Tunaberg area in Sweden, and the Akchatau mine in Kazakhstan.

Rarity

Very rare

For collectors

## Quality Criteria The most prized specimens by collectors are those with well-formed, sharp crystals with a distinct metallic luster, forming aesthetic, radial aggregates. Contrast with the surrounding host rock (matrix), for example, white quartz, is important. Specimens with visible associations of rare minerals, such as pekoite or gladite, are particularly sought after. The size of the crystals, rarely exceeding a few millimeters, also affects the value. ## Popular Localities By far the most desirable and classic junoite specimens come from its type locality - the Juno mine in Tennant Creek, Australia. Material from this location is considered exemplary for this mineral species.

Care and storage

## Cleaning Junoite specimens should only be cleaned mechanically, using a soft brush to remove dust. Due to its softness and perfect cleavage, ultrasonic cleaners and hard tools should be avoided. Contact with water should be minimized, and after cleaning, the specimen should be thoroughly dried immediately. ## What to Avoid Avoid contact with acids and other chemicals that can react with sulfides and selenides, leading to damage to the mineral's surface. Junoite is susceptible to oxidation, so it should be protected from humid air, which can cause tarnishing and the formation of coatings. It should not be heated or exposed to rapid temperature changes. ## Storage It is recommended to store junoite in dry conditions, preferably in tightly sealed display boxes away from other minerals that could scratch it. Moisture absorbers should be used to minimize the risk of oxidation. Display should be in closed display cases, protecting against dust and humidity.

Sources

• IMA Mineral List (CNMNC)