Strassmannite
Chemical formula: Al(U<sup>6+</sup>O<sub>2</sub>)(S<sup>6+</sup>O<sub>4</sub>)<sub>2</sub>F·16H<sub>2</sub>O
Strassmannite is a rare, hydrated uranyl aluminum sulfate, forming microscopic, prismatic crystals of intense yellow color and fluorescence.
Properties
- Mohs hardness
- 2
- Luster
- Vitreous
- Streak
- Light yellow
- Density
- 2.61
- Cleavage
- Good on {010}
- Fracture
- Uneven
- Transparency
- Transparent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Characteristic features of strassmannite include its lemon-yellow color, the form of small, prismatic crystals forming radial aggregates, and very strong, greenish-yellow fluorescence under UV light. It occurs in paragenesis with other secondary uranium minerals. ## Differentiation from Similar Minerals It can be confused with other yellow, secondary uranium minerals, such as johannite, uranopilite, or zippeite. Definitive differentiation from these minerals is almost exclusively possible using advanced analytical methods, such as X-ray diffraction (XRD) or spectroscopy. ## Crystal Forms Strassmannite forms elongated, prismatic crystals, often flattened. They usually occur as small, radial or haphazardly tangled aggregates on the surface of the host rock.
Geological environment
## Genesis Strassmannite is a secondary mineral that forms as a result of weathering (oxidation) of primary uranium ores, mainly uraninite, in a sulfate-rich environment. It crystallizes from acidic mine waters under low-temperature conditions, most often on the walls of old mine workings or on waste dumps. ## Mineral Associations This mineral co-occurs with other secondary sulfates and uranyl sulfates. At the type locality (Schneeberg), it was found in association with gypsum, johannite, uranopilite, bieberite, eriachalcite, and epsomite. ## Localities The only confirmed and described occurrence of strassmannite in the world is its type locality – the waste dump of the "Weißer Hirsch" uranium mine in Schneeberg, in the Ore Mountains (Saxony, Germany).
Rarity
Very rare
For collectors
## Quality Criteria The collector's appeal of strassmannite specimens depends on the richness and aesthetics of the crystal aggregates on the rock matrix. Most valued are specimens with clearly visible, well-formed, radial groups of crystals that cover a significant surface area of the host rock. The intensity of color and strong fluorescence also enhance the visual value of the specimen. ## Popular Localities The only known source of strassmannite specimens is its type locality in Schneeberg, Germany. All materials available on the collector's market originate from this single location.
Care and storage
## Cleaning Strassmannite specimens should generally not be wet-cleaned. Due to its water solubility and delicate nature, contact with liquids can damage it. Only careful dust removal with a soft brush or a photographic air blower is permissible. ## What to Avoid Contact with water and other chemicals must be strictly avoided. The mineral is sensitive to changes in humidity and temperature. As a uranium mineral, it is radioactive – direct, prolonged skin contact should be avoided, and especially inhalation of dust. Always wash hands after contact with the specimen. ## Storage Strassmannite specimens should be stored in a dry place, preferably in a sealed, lockable "perky box" to protect them from dust, moisture, and mechanical damage. Due to its radioactivity, it should be kept away from areas of permanent human presence and marked with an appropriate label.