Borodaevite

Chemical formula: Ag<sub>4.83</sub>Fe<sub>0.21</sub>Pb<sub>0.45</sub>(Bi,Sb)<sub>8.84</sub>S<sub>16</sub>

Borodaevite is a rare silver, lead, and bismuth sulfosalt, forming acicular crystals with a metallic, steel-gray luster.

## Characteristics Borodaevite is a mineral from the sulfosalt group, crystallizing in the orthorhombic system. It occurs as elongated, acicular or fibrous crystals, often forming tangled or radial aggregates. Its color is steel-gray to lead-gray, with a distinct metallic luster on fresh surfaces. ## Physical Properties It is characterized by relatively low hardness, approximately 2.5-3 on the Mohs scale. It is a brittle and opaque mineral. It has a high density, reaching 7.3-7.4 g/cm³, which is easily noticeable even in small samples. It exhibits perfect cleavage in one direction. ## Colors and Varieties This mineral does not show color variation – it is always steel-gray or lead-gray. Over time, its surface may tarnish or become covered with a darker coating due to oxidation. No varieties are distinguished. ## History and Name The name borodaevite was given in honor of Yuri Sergeevich Borodaev (1930-2003), a Russian mineralogist and professor at the Department of Mineralogy of Moscow State University, known for his research on sulfosalts. The mineral was approved by the International Mineralogical Association (IMA) in 1982. ## Applications Due to its great rarity, borodaevite has no industrial applications. It is solely an object of interest for specialized collectors of rare minerals and scientists studying ore deposits.

Properties

Mohs hardness
2.5-3
Luster
Metallic
Streak
Black
Density
7.3-7.4
Cleavage
Perfect on {100}
Fracture
Uneven
Transparency
Opaque
Crystal system
Orthorhombic

Diagnostic features

## Identification Identification is based on its characteristic acicular or fibrous form, steel-gray color, metallic luster, and high density. Its occurrence in association with other rare ore minerals, especially in hydrothermal veins, is also crucial. ## Distinguishing from Similar Minerals Visually, it is almost impossible to distinguish from many other acicular sulfosalts, such as bismuthinite, stibnite, owyheeite, or jamesonite. Certain identification requires advanced analytical methods, such as X-ray microanalysis (EDS/WDS) or X-ray diffraction (XRD), which allow for the determination of its unique chemical composition (simultaneous presence of Ag, Pb, Bi, and Sb). ## Crystal Forms It forms prismatic, strongly elongated in one direction, acicular crystals. They usually occur in the form of radial, tangled, or fibrous aggregates, less often as single, well-formed needles.

Geological environment

## Genesis It is a mineral of hydrothermal origin. It forms in ore veins rich in silver, bismuth, lead, and antimony, forming under low and medium temperature conditions. ## Mineral Associations It co-occurs with minerals such as native gold, galena, hessite, petzite, sylvanite, altaite, quartz, pyrite, and other rarer sulfosalts. ## Localities The main and best-known locality is the type locality – the Ustarasaiskoe gold deposit in Uzbekistan. It has also been reported in several other places around the world, including the Nagybörzsöny mine in Hungary and the Kochbulak deposit, also in Uzbekistan.

Rarity

Very rare

For collectors

## Quality Criteria The collector's value of a specimen depends on the richness and development of the acicular aggregates. Samples where borodaevite forms distinct, dense clusters on the rock matrix are most prized. The presence of clearly visible associated minerals, especially native gold or rare tellurides, adds significant value. ## Popular Localities The most known and valued specimens come from the type locality in Uzbekistan (Ustarasaiskoe), where the best-formed crystals of this mineral originate.

Care and storage

## Cleaning Dry cleaning is recommended, using a soft brush to gently remove dust. Avoid contact with water and any chemical agents that could cause oxidation or damage. ## What to Avoid The mineral is soft, brittle, and susceptible to scratches. It should be protected from moisture, which can accelerate oxidation processes (tarnishing). Ultrasonic cleaners, acids, or other aggressive chemicals should not be used. ## Storage It is best to store it in a closed, stable environment, e.g., in a "micromount" box or in a display case away from other, harder minerals. This method of storage protects delicate, acicular crystals from mechanical damage, dust, and moisture.

Sources

Read more