Klebelsbergite

Chemical formula: Sb³⁺₄O₄(S⁶⁺O₄)(OH)₂

Klebelsbergite is a rare antimony sulfate, forming characteristic, acicular crystals of a lemon-yellow color.

## Characteristics Klebelsbergite is a secondary antimony mineral, occurring as fine, acicular or hair-like crystals. It typically forms radial aggregates, crusts, or coatings on other minerals. Crystals are most often colorless, white, pale yellow, or lemon-yellow, which is its most recognizable visual feature. Due to the small size of the crystals, its features are often difficult to observe with the naked eye. ## Physical Properties This mineral is characterized by a silky or vitreous luster. It is relatively soft, with a Mohs hardness of approximately 3.5. It is transparent to translucent. The density of klebelsbergite is significantly higher than average, around 4.7 g/cm³, which is typical for minerals containing heavy elements like antimony. ## Colors and Varieties Klebelsbergite occurs in a limited color range, from colorless, through white, to various shades of yellow, with the most characteristic being lemon-yellow. No distinct color varieties or commercial varieties are recognized. ## History and Name The mineral's name honors Count Kuno Klebelsberg (1875–1932), a Hungarian politician, minister of culture and education. The mineral was first described in 1929 based on specimens found in Baia Sprie (Felsőbánya), Romania. ## Uses Klebelsbergite has no industrial applications. Its significance is purely scientific and as a collector's item; it is valued by collectors specializing in rare minerals or secondary minerals from oxidation zones.

Properties

Mohs hardness: 3.5-4
Color: Dark yellow; colourless to yellow in transmitted light.
Luster: Silky
Streak: White to yellow
Density: 4.62
Cleavage: Perfect on {100}
Fracture: Uneven
Transparency: Transparent
Crystal system: Orthorhombic

Diagnostic features

## Identification Klebelsbergite is most easily recognized by its characteristic mode of occurrence – as fine, acicular or hair-like crystals forming radial aggregates. The lemon-yellow color is also a strong diagnostic indicator. Due to the small size of the crystals, a magnifying glass or microscope is often necessary for identification. ## Distinguishing from Similar Minerals It can be confused with other yellow secondary antimony minerals, such as stibiconite or bindheimite. Differentiation often requires advanced analytical methods (XRD, EDS), but klebelsbergite is distinguished by its form of thin, acicular crystals, whereas other antimony oxides more often form earthy aggregates or massive crusts. ## Crystal Forms Klebelsbergite crystals are elongated along the [001] axis and have an acicular or hair-like habit. They usually occur as radial or tangled aggregates, as well as delicate coatings and crusts.

Geological environment

## Genesis Klebelsbergite is a secondary mineral, forming in the oxidation zones of hydrothermal ore deposits rich in antimony, especially in deposits containing stibnite (Sb₂S₃). It forms as a result of weathering and alteration of primary antimony sulfides under low temperature and pressure conditions. ## Mineral Associations It most often co-occurs with minerals from which it forms or which accompany it in the oxidation process. These are primarily stibnite, stibiconite, senarmontite, valentinite, as well as native sulfur, barite, and quartz. ## Localities The most important and classic localities for this mineral are Baia Sprie and Baia Mare in Romania. It is also known from the Fichtelgebirge mine in Bavaria (Germany), from Pereta (Tuscany, Italy), from Příbram in the Czech Republic, and from several locations in Japan and Bolivia. However, these occurrences are mainly of scientific significance.

Rarity

Very rare

For collectors

## Quality Criteria Specimens with well-formed, radial aggregates of acicular crystals of intense, lemon-yellow color are most valued by collectors. Contrast with the rock matrix and lack of damage to the delicate crystals are important. Due to its rarity, even small micromounts are sought after. ## Popular Localities Specimens from the classic locality in Baia Sprie, Romania, are considered exemplary and most desired by collectors specializing in mineral systematics.

Care and storage

## Cleaning Klebelsbergite specimens are extremely delicate and brittle. They should be cleaned only very carefully, using compressed air to remove dust. Any contact with water or a brush can irreversibly damage the fine, acicular crystals. Ultrasonic cleaning is not recommended. ## What to Avoid Avoid contact with all chemicals, including acids and bases. The mineral is sensitive to shocks and mechanical damage. It should be protected from moisture and sudden temperature changes. ## Storage Specimens should be stored in sealed, padded "micromount" boxes to protect them from dust, moisture, and mechanical damage. They should not be exposed to direct sunlight, although no particular light sensitivity is known.

External references

https://www.mindat.org/min-2223.html