Tetraferriphlogopite
Chemical formula: KMg<sub>3</sub>(Si<sub>3</sub>Fe<sup>3+</sup>)O<sub>10</sub>(OH)<sub>2</sub>
Tetraferriphlogopite is a mineral from the mica group, an iron-rich analog of phlogopite, characterized by its dark color and platy habit.
Properties
- Mohs hardness
- 2.5-3
- Luster
- Vitreous, Pearly
- Streak
- Greyish green
- Density
- 2.86
- Cleavage
- Perfect on {001}
- Fracture
- Uneven
- Transparency
- Translucent to opaque
- Crystal system
- Monoclinic
Diagnostic features
## Identification Tetraferriphlogopite is primarily identified by its characteristic platy or scaly habit, pseudohexagonal crystal outline, excellent cleavage in one direction, and dark, brown to black color. Thin lamellae separated from the main specimen are flexible. ## Distinguishing from Similar Minerals It can be confused with other dark-colored micas, mainly biotite and phlogopite. Differentiation from phlogopite requires chemical analysis to confirm the high iron content in the tetrahedral position. It differs from biotite by subtle optical and chemical properties, making definitive identification possible only through laboratory methods such as X-ray diffraction (XRD) or X-ray microanalysis (EDS/WDS). ## Crystal Forms Crystals are tabular, with a pseudohexagonal outline. It most often occurs as platy, scaly, or radial aggregates. Well-formed, isolated crystals are rare.
Geological environment
## Genesis Tetraferriphlogopite is a high-temperature mineral. It forms in metasomatic and metamorphic processes, especially in potassium- and magnesium-rich, aluminum-poor rocks, such as skarns, fenites, or carbonatites. It can also crystallize in some ultramafic igneous rocks. ## Mineral Associations It often co-occurs with minerals such as calcite, dolomite, diopside, forsterite, apatite, magnetite, and other minerals from the mica group. ## Localities Known occurrences of tetraferriphlogopite include alkaline rock and carbonatite complexes. Important localities include the vicinity of Vesuvius in Italy, the Kovdor massif on the Kola Peninsula in Russia, as well as occurrences in Norway, Canada (Quebec), and the United States.
Rarity
Rare
For collectors
## Quality Criteria Specimens with well-formed, sharp crystals with a pseudohexagonal outline are most valued by collectors. Crystal size and luster are also important. Aesthetic compositions with other contrasting minerals, such as white calcite, are also attractive. Purity and lack of mechanical damage to the delicate lamellae are crucial. ## Popular Localities Specimens of particular collectible value come from classic localities, such as the Somma-Vesuvius volcanic complex in Italy, known for its well-formed crystals. Specimens from the Kovdor massif in Russia are also highly prized.
Care and storage
## Cleaning Tetraferriphlogopite specimens should be cleaned very carefully. It is best to use compressed air to remove dust. If necessary, a soft, dry brush can be used. Avoid contact with water, which can penetrate between the lamellae and cause them to delaminate. ## What to Avoid Avoid all chemicals, including acids and strong bases. The mineral is soft and susceptible to scratching. The lamellae are brittle and easily damaged mechanically. Do not subject it to ultrasound or sudden temperature changes. ## Storage Specimens should be stored in separate, padded boxes to prevent scratching and damage to the delicate lamellae. They should be protected from dust and moisture. It is not sensitive to sunlight.