Goslarite

Chemical formula: Zn²⁺S⁶⁺O₄·₇H₂O

Goslarite is a hydrated zinc sulfate, forming white, acicular efflorescences and coatings, primarily occurring in the oxidation zones of zinc ores.

## Characteristics Goslarite is a hydrated zinc sulfate belonging to the epsomite group. It most commonly occurs as efflorescences, coatings, and crusts of fibrous, acicular, or hair-like habit. It also forms granular, botryoidal aggregates, and stalactitic incrustations. Well-formed, small crystals of prismatic or tabular habit are rarely observed. It is an unstable mineral, readily soluble in water and hygroscopic – it absorbs moisture from the air, which can lead to its dissolution. ## Physical Properties Goslarite is very soft, with a Mohs hardness of 2-2.5. It has a relatively low density, around 2.0 g/cm³. This mineral is characterized by a vitreous or silky luster. It is brittle, and its fracture is conchoidal. It possesses perfect cleavage in one direction. ## Colors and Varieties It is most often colorless or white. Impurities can impart yellowish, greenish, bluish, or reddish-brown hues, originating from inclusions of other minerals or metal ions such as copper or iron. No named varieties of goslarite are distinguished, although specimens with varying coloration depending on the admixtures are encountered. ## History and Name The name goslarite comes from the historic mining town of Goslar in Lower Saxony, Germany, where this mineral was found in the Rammelsberg mines. It was first described in 1847 by the Austrian mineralogist Wilhelm Haidinger. ## Uses Due to its instability and water solubility, goslarite has no direct industrial or jewelry applications. However, it is an important object of interest for collectors of secondary minerals and systematic specimens. It also serves as an indicator of the presence of zinc deposits.

Properties

Mohs hardness: 2-2.5
Color: Colourless; light brown, green or blue; white; colourless in transmitted light.
Luster: Vitreous
Streak: White
Density: 1.978
Cleavage: On {010}, perfect.
Fracture: Conchoidal
Transparency: Transparent
Crystal system: Orthorhombic

Diagnostic features

## Identification Goslarite is most easily identified by its typical forms of occurrence – white, hair-like or acicular efflorescences and coatings on rocks or other minerals. A key diagnostic feature is its extreme solubility in water. It also has a characteristic, astringent and metallic taste (taste testing is not recommended for safety reasons). It is very soft and light. ## Distinguishing from Similar Minerals Goslarite can be confused with other secondary sulfates, such as epsomite (magnesium sulfate) or melanterite (iron sulfate). Epsomite has a very similar appearance but a bitter taste. Melanterite often has a greenish or bluish coloration and weathers over time to yellowish-brown products. Chalcotrichite (a variety of cuprite, not a sulfate) also forms white, acicular aggregates, but is associated with pyrite. Final distinction often requires chemical analysis. ## Crystal Forms It most commonly occurs as fibrous, acicular, hair-like aggregates (so-called "zinc wool") and as coatings and crusts. It also forms stalactites and botryoidal aggregates. Single, well-formed orthorhombic crystals are rarely found; these are usually small and have a columnar or tabular habit.

Geological environment

## Genesis Goslarite is a typical secondary mineral. It forms as a result of the oxidation (weathering) of sulfide zinc ores, mainly sphalerite, in a dry and well-ventilated environment, such as old mine workings, adits, and mine dumps. It crystallizes from sulfate solutions under conditions of low humidity. ## Mineral Associations It most often co-occurs with the mineral from which it forms – sphalerite. It is also accompanied by other secondary sulfates, such as melanterite, epsomite, chalcanthite, as well as gypsum, anglesite, smithsonite, and hemimorphite. ## Localities Significant goslarite localities worldwide include the Rammelsberg mine near Goslar in Germany (type locality), Falun in Sweden, mines in the Potosí region of Bolivia, Chañarcillo in Chile, as well as numerous localities in the USA (e.g., Leadville in Colorado, Utah, and Arizona). In Poland, its occurrence has been noted in old zinc and lead ore mines in Upper Silesia (e.g., in the Bytom and Tarnowskie Góry areas) and in the Świętokrzyskie Mountains.

Rarity

Not very common

For collectors

## Quality Criteria Most valued by collectors are specimens with well-formed, long, and clean "hairs" or needles, forming dense, fluffy aggregates. The attractiveness is enhanced by a contrasting matrix on which the white goslarite fibers grow. Rare, well-formed, single crystals, despite their small size, are also highly sought after. Purity (lack of impurities and discoloration) and the size and abundance of aggregates are key factors influencing the value of a specimen. ## Popular Localities Classic and historically important specimens come from the Rammelsberg mine in Germany. Currently, spectacular specimens from Bolivia, Peru, and some mines in the United States appear on the collector's market. These specimens are often characterized by a high abundance and purity of fibrous aggregates.

Care and storage

## Cleaning Goslarite is extremely sensitive to water and moisture. It must absolutely not be cleaned with water or any liquids, as it will dissolve. The only safe method is to very gently remove dust using a soft, dry brush or a stream of compressed air from a distance. ## What to Avoid Avoid contact with water, water vapor, and any moisture. The mineral is hygroscopic, meaning it absorbs moisture from the surroundings, leading to its degradation. Protect it from temperature changes, which can cause water vapor condensation. Do not use any chemical agents. ## Storage Goslarite specimens must be stored in conditions of controlled, low humidity. The best solution is a sealed, airtight container (e.g., a "perky box") with a desiccant such as silica gel. Avoid exposure to open air.