Anthoinite
Chemical formula: AlW<sup>6+</sup>O<sub>3</sub>(OH)<sub>3</sub>
Anthoinite is a rare, secondary tungsten mineral, forming microscopic, white or colorless earthy aggregates.
Properties
- Mohs hardness
- 1
- Luster
- Earthy
- Streak
- White
- Density
- 3.6
- Cleavage
- Perfect on {100}
- Fracture
- Uneven
- Transparency
- Opaque
- Crystal system
- Triclinic
Diagnostic features
## Identification Anthoinite is difficult to identify without advanced analytical methods, such as X-ray diffraction (XRD). In field conditions or in a collection, it can be suspected based on its appearance – white, chalk-like, and very soft coatings or masses in the oxidation zones of tungsten deposits, especially in association with ferberite or scheelite. ## Distinguishing from similar minerals It can be confused with other secondary tungsten minerals, such as hydrotungstite, as well as with clay minerals (e.g., kaolinite) or other earthy coatings. Kaolinite, however, is much lighter. Certain distinction from similar tungsten oxides and hydroxides requires chemical analysis. ## Crystal forms It forms exclusively microscopic, bladed or tabular crystals, which combine into earthy, powdery, or chalk-like aggregates and coatings.
Geological environment
## Genesis Anthoinite is a secondary mineral, formed by the weathering and oxidation of primary tungsten minerals, mainly ferberite and scheelite. It forms in the oxidation zones (iron caps) of tungsten-bearing deposits, often in quartz veins. ## Mineral associations It most often co-occurs with the mineral from which it formed – ferberite. It is also accompanied by quartz, muscovite, as well as other secondary tungsten and iron minerals, such as goethite, hematite, tungstite, and hydrotungstite. ## Localities The most important and type locality is the Kilo gold and tungsten mine, in Ituri Province, Democratic Republic of Congo. It has also been reported in small quantities at the Wolfram Camp mine in Queensland, Australia, and in several locations in Brazil.
Rarity
Very rare
For collectors
## Quality criteria The quality of anthoinite specimens is assessed mainly based on the richness and purity of the coating on the host rock. Since it is a microscopic mineral, specimens where anthoinite forms distinct, thick, and well-defined aggregates, contrasting with the substrate, are most valued. Well-documented association with other minerals, especially ferberite, is also important. ## Popular localities By far the most classic and sought-after specimens come from the type locality in the Democratic Republic of Congo. Specimens from other locations are extremely rare and are a great treat for collectors specializing in mineral systematics.
Care and storage
## Cleaning Anthoinite specimens are extremely delicate and brittle. Mechanical cleaning or cleaning with water is not recommended, as it can destroy or dissolve the fine aggregates. The safest way to remove dust is with a gentle stream of air from a photographic blower bulb. ## What to avoid Avoid contact with water, chemicals, as well as any vibrations and impacts. The mineral is very soft and easily abrades or disintegrates. Store away from moisture. ## Storage It is recommended to store specimens exclusively in sealed, padded "micromount" boxes to protect them from mechanical damage, dust, and moisture. It is not suitable for display outside such protection.