Alumino-ferrowinchite
Chemical formula: ☐NaCa(Fe<sup>2+</sup>,Al)<sub>5</sub>Si<sub>8</sub>O<sub>22</sub>(OH)<sub>2</sub>
A very rare amphibole group mineral, the alumino-ferrous analogue of winchite, found in metamorphic rocks.
Properties
- Mohs hardness
- 5.5-6
- Luster
- Vitreous
- Streak
- Light grey
- Density
- 3.23
- Cleavage
- Good on {110}
- Fracture
- Uneven
- Transparency
- Translucent to Opaque
- Crystal system
- Monoclinic
Diagnostic features
## Identification Identification of alumino-ferrowinchite based on visual characteristics is impossible. As a dark, prismatic mineral, it is indistinguishable from many other amphiboles. Definitive identification requires advanced analytical methods, such as X-ray microanalysis (EDS/WDS) to determine the exact chemical composition and X-ray diffraction (XRD) to confirm the crystal structure. ## Distinguishing from Similar Minerals Visually, it cannot be distinguished from other dark amphiboles, such as arfvedsonite, ferro-richterite, and especially from other minerals in the winchite group. The differences between them are purely chemical and concern the proportions of sodium, calcium, magnesium, iron, and aluminum in the structure. ## Crystal Forms It most often forms columnar or acicular crystals with a rhombic cross-section. These crystals often arrange themselves into radial or fibrous aggregates embedded in the host rock.
Geological environment
## Genesis It is a mineral typical of rocks that have undergone metamorphism under specific pressure and temperature conditions. It primarily forms in metamorphosed, manganese-rich sediments. ## Mineral Associations At the type locality (Kajlidongri, India), it coexists with minerals such as braunite, quartz, bixbyite, hollandite, piemontite, and other manganese amphiboles and pyroxenes. ## Localities The most important and well-documented occurrence of alumino-ferrowinchite in the world is the Kajlidongri manganese mine in the Jhabua district, Madhya Pradesh, India. This is its type locality, from which most studied specimens originate.
Rarity
Very rare
For collectors
## Quality Criteria As a microscopic mineral, its collector's value depends on several factors. Specimens with well-formed, sharp microcrystals forming rich aggregates on a small rock matrix are most highly prized. An additional advantage is the coexistence with other rare minerals, which increases the scientific and aesthetic value of the specimen. ## Popular Localities Virtually all specimens available on the collector's market come from a single location - the Kajlidongri mine in India. This is the only locality providing material in quantities that allow for distribution among collectors specializing in rare minerals.
Care and storage
## Cleaning Specimens should only be cleaned mechanically, using a soft brush. If necessary, distilled water can be used. Ultrasonic cleaners should be avoided, as they can damage delicate, fibrous aggregates. ## What to Avoid The mineral is sensitive to strong acids. Avoid sudden temperature changes. It is not particularly sensitive to light, but prolonged exposure to direct sunlight is not recommended for any mineral. ## Storage Specimens, especially those in the form of micromounts, should be stored in closed display boxes to protect them from dust and mechanical damage. It is stable under typical room conditions.