Xenophyllite
Chemical formula: Na<sub>4</sub>Fe<sup>2+</sup><sub>7</sub>(PO<sub>4</sub>)<sub>6</sub>
Xenophyllite is a very rare sodium and iron phosphate, forming characteristic, lamellar aggregates of a dark green color.
Properties
- Mohs hardness
- 4
- Luster
- Vitreous, Pearly
- Streak
- Greenish gray
- Density
- 3.69
- Cleavage
- Perfect on {0001}
- Transparency
- Translucent
- Crystal system
- Trigonal
Diagnostic features
## Identification Key diagnostic features of xenophyllite include its dark green color, characteristic lamellar or scaly habit, often in the form of rosettes, and perfect cleavage in one direction. Its specific occurrence environment – alteration zones in granitic pegmatites, in association with other rare phosphates – is also an important indicator. ## Distinguishing from Similar Minerals Xenophyllite can be confused with other minerals of similar appearance, such as some chlorites (e.g., chamosite) or micas (e.g., biotite). Differentiation based on visual characteristics is difficult. However, xenophyllite is distinguished by its higher density and mineral paragenesis. Certain differentiation requires advanced analytical methods, such as X-ray diffraction (XRD). ## Crystal Forms Xenophyllite forms tabular, hexagonal crystals, most often occurring as lamellar, scaly, or bladed aggregates. Rosette-like or fan-like aggregates are characteristic.
Geological environment
## Genesis Xenophyllite is a secondary mineral, formed as a result of hydrothermal processes in the late stages of crystallization of complex granitic pegmatites. It forms in alteration zones where primary phosphates undergo transformations under the influence of sodium-rich solutions. ## Mineral Associations This mineral co-occurs with other, often rare, phosphates. Its typical associated minerals include strengite, rockbridgeite, beraunite, dufrénite, ludlamite, vivianite, mitridatite, and anapaite. ## Localities Xenophyllite is an extremely rare mineral. The most important and typical locality for its occurrence is the Angarf-Sud pegmatite near Tazenakht in Morocco. This is the main and practically only locality from which specimens of collector's significance originate.
Rarity
Very rare
For collectors
## Quality Criteria The most valued by collectors are specimens with well-formed, sharp rosettes or fans of lamellar crystals. Intense, dark green color and the placement of aggregates on a contrasting rock matrix are highly appreciated. Association with other rare phosphates is also of great importance, increasing the scientific and aesthetic value of the specimen. ## Popular Localities The only known source of high-quality xenophyllite specimens is the Angarf-Sud pegmatite in Morocco. Specimens from this locality are considered the best in the world and serve as a reference for this mineral.
Care and storage
## Cleaning Xenophyllite specimens are delicate due to their perfect cleavage and lamellar structure. For dust removal, it is best to use a soft brush or compressed air from a safe distance. If necessary, the specimen can be very carefully rinsed in distilled water, then immediately and thoroughly dried. Ultrasonic cleaners should be avoided. ## What to Avoid The mineral is sensitive to acids and strong chemicals. It should be protected from mechanical damage, impacts, and scratching, as its lamellae easily separate. Prolonged exposure to moisture can lead to slow chemical changes. ## Storage It is recommended to store specimens in separate, padded boxes to protect delicate aggregates from crumbling. A dry and stable environment, away from direct sunlight and sudden temperature changes, is best.