Ferri-hellandite-(Ce)
Chemical formula: (Ca₃Ce³⁺)Ce³⁺₂Fe³⁺◻₂B₄Si₄O₂₂(OH)₂
Ferri-hellandite-(Ce) is a rare borosilicate from the hellandite group, forming brown, prismatic crystals in alkaline pegmatites.
Properties
- Mohs hardness
- 5.5
- Luster
- Vitreous
- Streak
- Light brown
- Density
- 3.75
- Cleavage
- Good on {010}
- Fracture
- Uneven
- Transparency
- Translucent to opaque
- Crystal system
- Monoclinic
Diagnostic features
## Identification Ferri-hellandite-(Ce) can be identified by its characteristic habit of long, prismatic crystals, often forming radial aggregates. The brown color, vitreous luster, and occurrence in alkaline pegmatites are key indicative features. ## Differentiation from Similar Minerals It can be confused with other minerals from the hellandite group or with tourmaline (schorl), but it differs from them in crystal habit and specific occurrence environment. Final differentiation from other hellandites requires advanced chemical analyses (EDS/WDS) to determine the dominant rare earth elements and the Fe/Al ratio. ## Crystal Forms Crystals are elongated and prismatic, reaching several centimeters in length. They usually occur in radial or fan-shaped aggregates, embedded in the host rock, most often in quartz or albite.
Geological environment
## Genesis Ferri-hellandite-(Ce) is a magmatic mineral, crystallizing in the late stages of the evolution of alkaline pegmatites, rich in rare earth elements and boron. It forms in an environment with a high concentration of these elements. ## Mineral Associations This mineral co-occurs with quartz, albite, microcline, aegirine, magnetite, titanite, zircon, allanite-(Ce), and fergusonite-(Y). ## Localities The most important and type locality (località tipo) is the Östanmossa quarry in the Norberg municipality, Västmanland region, Sweden. This is the only confirmed and detailed described locality for this mineral in the world.
Rarity
Very rare
For collectors
## Quality Criteria The most prized specimens are those with well-formed, sharply terminated crystals of intense brown color, forming aesthetic, radial aggregates. Contrast with a light host rock (e.g., white albite or quartz) is also important. Specimens with visible, undamaged crystals exceeding one centimeter in length are considered high quality. ## Popular Localities The only source of collector specimens is the Östanmossa quarry in Sweden. Material from this locality is extremely rare on the market and sought after by specialized collectors of pegmatite and rare earth element minerals.
Care and storage
## Cleaning It is recommended to clean specimens only with a soft brush to remove dust. The use of water, especially with detergents, is not advisable due to a lack of data on its effect on the mineral. ## What to Avoid Avoid contact with chemicals, acids, and cleaning agents. The mineral should be protected from ultrasound and sudden temperature changes. It should not be exposed to prolonged direct sunlight. ## Storage Specimens should be stored in stable conditions, in individual, padded boxes to prevent scratches and mechanical damage. It is best to keep them away from moisture and dust.