Ferro-ferri-holmquistite
Chemical formula: ◻Li₂(Fe²⁺₃Fe³⁺₂)(Si₈O₂₂)(OH)₂
A rare, dark-colored lithium amphibole, found in lithium-rich pegmatites and metamorphic rocks.
Properties
- Mohs hardness
- 5.5
- Color
- Blue
- Luster
- Vitreous
- Streak
- Bluish-grey
- Density
- 3.32
- Cleavage
- On {210}.
- Fracture
- Uneven
- Transparency
- Opaque
- Crystal system
- Orthorhombic
Diagnostic features
## Identification Identification of ferro-ferri-holmquistite requires advanced research methods, such as chemical analysis (EDS/WDS) to confirm the dominance of Fe²⁺ and Fe³⁺ and lithium content. It can be preliminarily recognized by its dark blue to black color, prismatic or fibrous habit, and occurrence in lithium pegmatites. ## Distinguishing from Similar Minerals This mineral is difficult to distinguish from other dark amphiboles, such as arfvedsonite, riebeckite, or other minerals from the holmquistite series, without specialized testing. Arfvedsonite and riebeckite often have a more vitreous luster and a slightly different crystal habit. Final differentiation is only possible based on chemical composition analysis. ## Crystal Forms Most commonly, it forms elongated, columnar, or acicular crystals. It also occurs as fibrous, matted (asbestos-like), and radial rosette aggregates.
Geological environment
## Genesis Ferro-ferri-holmquistite is a mineral of metamorphic and magmatic origin. It forms in contact zones of lithium-rich granitic pegmatites with ultramafic rocks (e.g., serpentinites) or amphibolites. This process, known as lithium metasomatism, leads to the enrichment of surrounding rocks in lithium and the formation of rare lithium minerals. ## Mineral Associations It often co-occurs with quartz, microcline, albite, talc, biotite, and other minerals from the holmquistite group. ## Localities The most important and well-documented occurrences of this mineral are in Canada, in Quebec province (Quebec Lithium mine, La Corne) and Ontario (Georgia Lake area). It has also been reported from several other locations worldwide, but these are occurrences of purely scientific significance.
Rarity
Very rare
For collectors
## Quality Criteria The most valued specimens by collectors are those with well-formed, large crystals of intense, dark blue color. Radial aggregates or specimens showing clear association with other minerals, such as quartz or talc, are also attractive. Due to its rarity, every well-documented specimen has collector's value. ## Popular Localities The vast majority of specimens available on the collector's market come from the Quebec Lithium mine in Canada. Specimens from this locality are considered reference material for this mineral species.
Care and storage
## Cleaning Specimens should only be cleaned mechanically, using a soft, dry brush or a small brush to remove dust. For heavier dirt, compressed air can be used. Avoid water and any chemical agents. ## What to Avoid Avoid contact with water, acids, and other chemicals that may react with the mineral. Fibrous forms are brittle and susceptible to mechanical damage. Do not heat or expose to sudden temperature changes. ## Storage Specimens, especially those with a fibrous structure, should be stored in sealed boxes or display cases to protect them from dust and mechanical damage. Avoid storage in humid environments.