Clino-ferro-ferri-holmquistite
Chemical formula: ☐Li<sub>2</sub>(Fe<sup>2+</sup><sub>3</sub>Fe<sup>3+</sup><sub>2</sub>)Si<sub>8</sub>O<sub>22</sub>(OH)<sub>2</sub>
A rare lithium amphibole of the holmquistite group, characterized by the dominance of iron in both +2 and +3 oxidation states.
Properties
- Mohs hardness
- 5-6
- Luster
- Vitreous
- Streak
- Grayish blue
- Density
- 3.33
- Cleavage
- Perfect on {210}
- Fracture
- Uneven
- Transparency
- Opaque, translucent in thin splinters
- Crystal system
- Monoclinic
Diagnostic features
## Identification Clino-ferro-ferri-holmquistite is difficult to identify unambiguously visually. Key features include its dark blue to black color, prismatic crystal habit, occurrence as radial aggregates, and a geological environment typical of amphiboles (lithium pegmatites). The streak is grayish-blue. Final confirmation requires advanced chemical (e.g., EDS) and X-ray (XRD) analyses to determine its composition and structure. ## Distinguishing from Similar Minerals It can be confused with other dark amphiboles, such as riebeckite, arfvedsonite, or other minerals from the holmquistite group. It differs from riebeckite and arfvedsonite by the presence of lithium in its composition. From other minerals of the holmquistite group (e.g., ferro-holmquistite), it is distinguished by the ratio of Fe²⁺ to Fe³⁺, which is impossible to determine without specialized analysis. ## Crystal Forms Crystals are typically elongated, prismatic, with hexagonal or octagonal cross-sections. They often form fibrous, radial aggregates or granular masses.
Geological environment
## Genesis It is an igneous mineral, forming in the late stages of crystallization of lithium-rich granitic pegmatites. It forms through metasomatism, i.e., the reaction of lithium-rich fluids with minerals of surrounding rocks, such as amphibolites or ultramafic rocks. ## Mineral Associations It most commonly co-occurs with quartz, microcline, albite, as well as other lithium minerals such as spodumene, lepidolite, or elbaite (tourmaline). It may also accompany other amphiboles. ## Localities The most important and best-documented occurrence of this mineral, which is also its type locality, is the Pedriza quarry near Nuevo Baztán, in the autonomous community of Madrid, Spain. This is the only confirmed locality in the world from which well-studied specimens originate.
Rarity
Very rare
For collectors
## Quality Criteria The collecting appeal of a specimen depends on the development and size of the crystals and their arrangement in the rock matrix. Well-defined, elongated crystals with an intense, dark blue color, forming radial aggregates on a light background of the host rock (e.g., on quartz or albite), are most valued. The presence of associated minerals that confirm the paragenesis is also important. ## Popular Localities The only source of collectible specimens is the type locality – the Pedriza quarry in Spain. Material from this location is extremely rare on the market.
Care and storage
## Cleaning Specimens should only be cleaned mechanically, using a soft, dry brush or paintbrush to remove dust. If necessary, compressed air can be used. Avoid contact with water and any chemical agents. ## What to Avoid Avoid ultrasonic cleaners, which can damage the specimen due to its cleavage. The mineral is sensitive to acids. It should not be heated or exposed to sudden temperature changes. ## Storage Specimens should be stored in stable conditions, in a dry place, away from direct sunlight. It is best to place them in a closed display box or cabinet to protect them from dust and mechanical damage.