Ferroberaunite
Chemical formula: Fe²⁺Fe³⁺₅(PO₄)₄(OH)₅·6H₂O
Ferroberaunite is a rare, hydrated iron phosphate, forming characteristic radial aggregates of green or greenish-brown color.
Properties
- Mohs hardness
- 3-4
- Luster
- Vitreous
- Streak
- pale olive-green
- Density
- 2.94
- Cleavage
- parallel to {100}
- Fracture
- Irregular/Uneven
- Transparency
- Transparent,Translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification The key diagnostic feature of ferroberaunite is its characteristic radial aggregates of small, acicular crystals of green or greenish-brown color. A pale, olive-green streak is also an important indicator. Its occurrence in paragenesis with other secondary phosphates in the oxidation zones of iron deposits is a strong clue. ## Distinguishing from Similar Minerals Ferroberaunite can be confused with other minerals from the beraunite group (beraunite, eleonorite), from which distinction is practically only possible through advanced chemical analyses (e.g., EDS). It can also be similar to cacoxenite, which, however, forms tufts and bundles of yellow to brown color, rather than spherical aggregates. Other green phosphates, like rockbridgeite, are usually darker and more massive. ## Crystal Forms Most commonly, it forms radial, spherical, or hemispherical aggregates composed of small, acicular or bladed crystals. Single, well-formed crystals are extremely rare.
Geological environment
## Genesis Ferroberaunite is a secondary phosphate mineral. It forms in the oxidation zones of iron ore deposits, as well as in granitic pegmatites containing primary phosphates (e.g., triphylite), as a result of their hydrothermal or weathering alterations. ## Mineral Associations It often co-occurs with other secondary phosphate minerals, such as strengite, rockbridgeite, dufrenite, beraunite, as well as goethite, hematite, and quartz. ## Localities The type locality (place of first discovery and description) is Gravel Hill Mine in Cornwall (United Kingdom). Other known occurrences include various localities in Germany (e.g., Clara Mine in the Black Forest, Hagendorf in Bavaria), the Czech Republic, Portugal, and the USA (e.g., South Dakota).
Rarity
Rare
For collectors
## Quality Criteria The most prized specimens by collectors are those with well-formed, distinct, spherical aggregates of intense green color. Contrast with the rock matrix (e.g., with quartz or goethite) is important. The size of the aggregates and the absence of mechanical damage significantly increase the value of the specimen. Purity, meaning the absence of undesirable coatings, is also essential. ## Popular Localities Specimens from classic localities in Germany (e.g., Rotläufchen Mine in Waldgirmes, Hagendorf-Süd) and from the type locality in Cornwall are sought after by specialists collecting phosphate minerals.
Care and storage
## Cleaning Specimens should be cleaned very carefully, preferably using a soft brush to remove dust. If necessary, compressed air can be used from a safe distance. Due to its fragility and possible reactivity, avoid washing in water, especially tap water. ## What to Avoid Avoid contact with all chemicals, including acids and strong bases, which can damage the mineral. It is sensitive to impacts and scratches. Protect it from high temperatures, which can lead to dehydration and structural changes. ## Storage It is recommended to store specimens in dry conditions, in sealed boxes or display cases, to protect them from dust and mechanical damage. It is best to keep it away from other, harder minerals to prevent scratching.