Davreuxite
Chemical formula: Mn<sup>2+</sup>Al<sub>6</sub>Si<sub>4</sub>O<sub>17</sub>(OH)<sub>2</sub>
Davreuxite is a rare manganese and aluminum silicate, forming fibrous or lamellar aggregates with a silky luster, found in metamorphic rocks.
Properties
- Mohs hardness
- 5.5
- Luster
- Silky
- Streak
- White
- Density
- 3.23-3.33
- Cleavage
- Perfect on {010}
- Fracture
- Uneven
- Transparency
- Translucent to opaque
- Crystal system
- Monoclinic
Diagnostic features
## Identification A characteristic feature of davreuxite is its fibrous or lamellar aggregates with a silky luster. The flexibility of individual fibers or thin lamellae is also helpful in identification. It occurs in a specific geological environment - aluminum-rich metamorphic rocks. ## Distinguishing from Similar Minerals Davreuxite can be confused with other fibrous silicates, such as tremolite, serpentine (chrysotile), or sillimanite. It is often distinguished from tremolite and serpentine by its geological context (co-occurrence with quartz, rutile, hematite). Sillimanite can be very similar, but davreuxite is significantly softer (sillimanite hardness is 6.5-7.5). Accurate differentiation often requires advanced analytical methods. ## Crystal Forms Crystals are monoclinic, lamellar or acicular in habit, elongated along one axis. They usually form radial, tangled, or fan-shaped aggregates. Single, well-formed crystals are rarely observed.
Geological environment
## Genesis Davreuxite is a mineral of metamorphic origin. It forms under conditions of low-grade metamorphism, in aluminum-rich sedimentary rocks (e.g., shales) that have been subjected to pressure and temperature. It is a typical component of quartz veins cutting through these rocks. ## Mineral Associations It most commonly co-occurs with quartz, hematite, rutile, as well as minerals from the chlorite group and kaolinite. In its type locality (Ottré, Belgium), it is found in association with quartz, hematite, and ottrelite. ## Localities The most important and classic locality, from which the best specimens originate, is Ottré in the Ardennes (Liège province, Belgium). This mineral has also been identified in several other locations worldwide, including the Kanto region in Japan, but it does not form such significant occurrences there as in Belgium.
Rarity
Rare
For collectors
## Quality Criteria The most valued by collectors are specimens from the classic locality in Ottré, Belgium. Rich, dense fibrous or radial aggregates with a distinct silky luster are considered attractive. A contrasting matrix, most often quartz, on which davreuxite aggregates are embedded, enhances the visual and collector value of the specimen. The size of the aggregates and their purity (absence of foreign coatings) are also important factors.
Care and storage
## Cleaning Davreuxite specimens should be cleaned very carefully, using a soft brush to remove dust. Due to its fibrous nature and potential fragility, washing in water, especially under pressure, should be avoided. If dirt removal is necessary, compressed air can be used from a safe distance. ## What to Avoid Contact with acids and other chemicals that may react with the mineral should be avoided. The fibrous structure is susceptible to mechanical damage, so the specimen should be protected from impacts, bending, and abrasion. It should not be heated or exposed to sudden temperature changes. ## Storage It is recommended to store specimens in closed, padded collector boxes to protect them from dust and mechanical damage. Heavier minerals should be avoided on delicate, fibrous davreuxite aggregates.