Simonkolleite

Chemical formula: Zn²⁺₅(OH)₈Cl₂·H₂O

Simonkolleite is a rare secondary zinc mineral, forming colorless or white, hexagonal crystals with a pearly luster.

## Characteristics Simonkolleite is a hydrated zinc hydroxychloride, belonging to the group of rare minerals. It occurs as small, tabular or platy crystals with a hexagonal outline. It most commonly forms rosette-like or fan-shaped aggregates, as well as coatings and efflorescences. Individual crystals are usually very small, rarely exceeding 1-2 mm, but can form striking, lustrous clusters on the surface of the host rock. ## Physical Properties This mineral is characterized by low hardness, measuring 2.5 on the Mohs scale. It is relatively light, and its crystals are flexible. It possesses perfect cleavage in one direction, which, combined with the pearly luster on the cleavage planes, is its characteristic feature. ## Colors and Varieties Simonkolleite is most often colorless or white. It can take on pale green, blue-green, or yellowish hues, which is usually caused by the presence of impurities, e.g., copper ions. No named varieties are distinguished. ## History and Name The mineral was first described in 1985 by Pete J. Dunn, Donald R. Peacor, Alan J. Criddle, and Chris J. Stanley. Its name honors Werner Simon (b. 1929) and Kurt Kolle (b. 1928), German mineral collectors from Warstein, who found the first samples of this mineral in the Richelsdorf quarry in Germany. ## Applications Simonkolleite has no industrial applications. It is solely an object of interest for collectors of rare minerals and scientists.

Properties

Mohs hardness: 1.5
Color: Colourless
Luster: Pearly to vitreous
Streak: White
Density: 3.20
Cleavage: {0001}
Fracture: Uneven
Transparency: Transparent,Translucent
Crystal system: Trigonal

Diagnostic features

## Identification The most important diagnostic features of simonkolleite are its characteristic, hexagonal, tabular crystals, often gathered in rosette-like aggregates. The pearly luster on basal planes, perfect cleavage in one direction, and low hardness are key for identification. It reacts vigorously with hydrochloric acid. ## Distinguishing from Similar Minerals Simonkolleite is sometimes confused with other secondary zinc minerals of similar appearance, such as hydrozincite. However, hydrozincite crystallizes in the monoclinic system and often exhibits strong, blue fluorescence under UV light, which simonkolleite does not possess. It can also be confused with gypsum or brucite, but it is distinguished from them by crystal shape and reaction with acids. ## Crystal Forms Crystals are thin-tabular, with a hexagonal outline, often arranged in fan-shaped, rosette-like, or spherulitic aggregates. It also occurs as fine-grained coatings and crusts.

Geological environment

## Genesis Simonkolleite is a secondary mineral, forming in the oxidation (weathering) zones of zinc ore deposits. It forms as a result of chloride-rich solutions acting on other zinc minerals, such as sphalerite. It is also found as a product of metallurgical activity, crystallizing on old dumps and slags, where zinc reacts with seawater or other chloride sources. ## Mineral Associations It most commonly co-occurs with other secondary zinc minerals, such as hydrozincite, hemimorphite, smithsonite, and aurichalcite. It also occurs in association with sphalerite, galena, gypsum, calcite, and quartz. ## Localities Important localities worldwide include the Richelsdorf quarry in Hesse (Germany), where it was discovered, and the Lavrion mine in Attica (Greece), from which numerous well-formed specimens originate. It is also found in mines in Namibia (Tsumeb), Australia (Broken Hill), Italy (Sardinia), and several localities in the USA (Arizona, Pennsylvania).

Rarity

Rare

For collectors

## Quality Criteria The most valued specimens by collectors are those with well-formed, sharp crystals with a distinct hexagonal outline, forming aesthetic, rosette-like aggregates. Samples where lustrous, pearly simonkolleite crystals contrast with the dark host rock are highly prized. The size of crystals and aggregates also significantly increases the value of a specimen, as does purity (lack of damage) and attractive associations with other minerals. ## Popular Localities The most famous and sought-after simonkolleite specimens come from the ancient mines in the Lavrion region of Greece. Classic specimens from the discovery locality in Richelsdorf, Germany, are also valued.

Care and storage

## Cleaning Simonkolleite specimens should be cleaned very carefully, using a soft brush to remove dust. Due to its reactivity, contact with water, especially acids, should be avoided. If liquid is necessary, pure, deionized water or alcohol is recommended, but with utmost caution and quick drying. ## What to Avoid The mineral is sensitive to chemicals, especially acids, in which it rapidly dissolves. Ultrasonic cleaners, which can destroy delicate crystals, should be avoided. It should not be heated or exposed to prolonged moisture. ## Storage Collector's specimens of simonkolleite are best stored in closed, dry containers (e.g., "membrane boxes") or display cases to protect them from dust, moisture, and mechanical damage. Due to its softness, it should not be stored in contact with harder minerals.