Calcioferrite
Chemical formula: Ca<sub>4</sub>MgFe<sup>3+</sup><sub>4</sub>(PO<sub>4</sub>)<sub>6</sub>(OH)<sub>4</sub>·12H<sub>2</sub>O
Calcioferrite is a hydrated calcium, magnesium, and iron phosphate, forming characteristic spherical or fibrous aggregates of a greenish color.
Properties
- Mohs hardness
- 2.5
- Luster
- Pearly to waxy
- Streak
- Pale yellow-green
- Density
- 2.53
- Cleavage
- Perfect on {010}
- Fracture
- Uneven
- Transparency
- Translucent
- Crystal system
- Triclinic
Diagnostic features
## Identification The most important diagnostic feature of calcioferrite is its mode of occurrence – characteristic spherical, botryoidal, or radiating-fibrous aggregates. Its specific greenish color, low hardness (can be scratched with a fingernail), and pearly or waxy luster also aid in identification. ## Distinguishing from Similar Minerals Calcioferrite is sometimes confused with other green secondary phosphates such as variscite, wavellite, or dufrénite. Wavellite often forms more distinct, star-shaped aggregates. Variscite is significantly harder (3.5-4.5 on the Mohs scale). Dufrénite typically has a darker, olive-green to almost black color. Definitive differentiation often requires advanced analysis, such as X-ray diffraction (XRD). ## Crystal Forms Calcioferrite crystals are microscopic and tabular, but extremely rare. This mineral almost always forms aggregates: spherical (spherulitic), reniform, botryoidal, and radiating-fibrous. It also occurs as thin crusts and coatings.
Geological environment
## Genesis Calcioferrite is a secondary mineral. It forms in the oxidation zones of iron ore deposits or, more commonly, as a result of hydrothermal alteration of primary phosphate minerals (mainly triphylite) in complex granitic pegmatites. ## Mineral Associations It often co-occurs with other phosphates, such as dufrénite, rockbridgeite, strengite, beraunite, vivianite, as well as with the primary mineral from which it forms – triphylite. Iron oxides, such as goethite, may also accompany it. ## Localities Key localities worldwide include: Battenberg in Hesse and the Hagendorf-Süd pegmatite in Bavaria (Germany); Tip Top Mine in South Dakota and Palermo No. 1 Mine in New Hampshire (USA); and the famous Sapucaia mine in Minas Gerais (Brazil). Occurrences have also been reported in the Czech Republic (Cyrilov in Moravia).
Rarity
Rare
For collectors
## Quality Criteria The collector's appeal of calcioferrite depends on several factors. Specimens with well-formed, spherical aggregates of an intense, apple-green color are most highly valued. The size of the spherulites and their quantity on the rock matrix are also important. Undamaged specimens with distinct structures and a contrasting matrix fetch higher prices. Co-occurrence with other rare phosphates adds value. ## Popular Localities Two localities are considered classic and yield the best specimens: the Hagendorf-Süd pegmatite in Germany and, above all, the Tip Top Mine in Custer County (South Dakota, USA). Specimens from the Tip Top Mine are renowned for beautiful, green calcioferrite spheres on a white matrix.
Care and storage
## Cleaning Calcioferrite specimens are soft and brittle, requiring great care. For dust removal, it is best to use a soft brush or compressed air from a safe distance. Avoid washing in water; if absolutely necessary, use a brief dip in distilled water and immediate, thorough drying. Under no circumstances should ultrasonic cleaners be used. ## What to Avoid The mineral is sensitive to chemicals, especially acids, which can damage it. As a hydrated mineral, it is also susceptible to structural changes due to high temperatures, which lead to dehydration. It should be protected from mechanical damage and scratching by harder minerals. ## Storage It is recommended to store specimens in separate, padded boxes or display cases, under stable room conditions, away from direct sunlight and heat sources. Exposure should provide protection from dust and mechanical damage.