Steverustite

Chemical formula: Pb²⁺₅Cu¹⁺(S⁶⁺O₃S²⁻)₃(OH)₅·₂H₂O

Steverustite is a very rare, secondary lead and copper mineral, distinguished by its unique chemical composition containing the thiosulfate anion.

## Characteristics Steverustite is a secondary mineral, forming in the oxidation zones of ore deposits. It occurs as very small, bladed or acicular crystals, rarely exceeding 0.2 mm in length. These crystals form rosetted or radiating aggregates, as well as thin coatings and crusts on other minerals. Due to the small size of the crystals, its visual features are difficult to observe without magnification. ## Physical Properties Steverustite crystals are flexible and can be bent. The Mohs hardness has not been precisely determined but is estimated to be around 2. The mineral has a luster described as silky to vitreous. It is transparent to translucent. The density calculated from the chemical formula and unit cell parameters is 5.45 g/cm³. ## Colors and Varieties Steverustite has a characteristic pale blue color. No varieties are known. ## History and Name The mineral was discovered on the dumps of the Endeavor Mine (also known as Elura Mine) near Cobar in New South Wales, Australia. It was approved by the International Mineralogical Association (IMA) in 2013 under number 2013-087. The name honors Steve Rust (born 1953), an Australian mineral collector who specializes in secondary minerals from the Broken Hill deposit and was the first to find specimens of the new mineral.

Properties

Mohs hardness: 2
Color: Colorless, white
Luster: Silky to Vitreous
Streak: White
Density: 5.150
Cleavage: Crystals were too small to observe cleavage.
Fracture: Splintery
Transparency: Transparent
Crystal system: Monoclinic

Diagnostic features

## Identification Steverustite is primarily recognized by its unique appearance – pale blue, silky aggregates composed of tiny, acicular crystals. Key to identification is its locality (Endeavor Mine) and co-occurrence with other rare secondary minerals such as anglesite and linarite. Final confirmation requires advanced analytical methods, such as Raman spectroscopy or X-ray diffraction. ## Distinguishing from Similar Minerals Steverustite can be confused with other pale blue secondary copper and lead minerals, such as linarite or some forms of aurichalcite. Linarite typically has a more intense, vibrant blue color. Aurichalcite forms similar acicular aggregates but often has a more greenish-blue or turquoise hue. Precise differentiation in the field is practically impossible without knowledge of the mineralogical context of the locality. ## Crystal Forms Crystals are very small, elongated in the form of blades or needles, reaching up to 0.2 mm in length and only a few micrometers in thickness. They form radiating, rosetted, or tangled aggregates, as well as thin coatings.

Geological environment

## Genesis Steverustite is a secondary mineral that forms as a result of weathering (oxidation) processes of sulfidic polymetallic deposits (lead, zinc, copper, and silver) in semi-arid climate conditions. Its unique composition, containing the thiosulfate ion (S₂O₃)²⁻, indicates specific, transitional chemical conditions (redox and pH) prevailing in the oxidation zone, where sulfides undergo slow decomposition. ## Mineral Associations This mineral occurs in paragenesis with other secondary sulfate and carbonate minerals. At the type locality (Endeavor Mine), it was found in association with anglesite, linarite, malachite, azurite, cerussite, hemimorphite, as well as rarer minerals such as brochantite, ammonium sulfate, beudantite, and kintoreite. ## Localities The only confirmed and described occurrence of steverustite in the world is the dumps of the Endeavor Mine (Elura Mine), located approximately 47 km north of Cobar in Robinson County, New South Wales, Australia.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of steverustite specimens is primarily assessed based on the richness and aesthetics of the crystalline aggregates. Most valued are specimens showing well-formed, albeit microscopic, rosettes or radiating clusters of acicular crystals with a distinct, pale blue color. Contrast with the rock matrix and the presence of rare associated minerals are also important. Due to the microscopic size of the crystals, specimens are primarily intended for collectors specializing in "micromount" type minerals. ## Popular Localities The only source of steverustite specimens is its type locality – the Endeavor Mine in Australia. All specimens available on the collector's market originate from this single location.

Care and storage

## Cleaning Steverustite specimens are extremely delicate and small. Any mechanical cleaning, including the use of brushes, should be avoided. If cleaning is absolutely necessary, compressed air can be carefully used from a safe distance. Contact with water, especially deionized water, can be risky due to potential solubility. ## What to Avoid Contact with acids and other chemicals must be strictly avoided. The mineral is sensitive to changes in temperature and humidity. It should not be heated or exposed to direct sunlight, which can cause dehydration and decomposition. ## Storage Specimens should be stored in stable conditions, preferably in closed, padded "micromount" boxes, which protect them from physical damage, dust, and sudden changes in humidity. Storage in a dry place is crucial for maintaining the mineral's integrity.

External references

https://www.mindat.org/min-38699.html