Akrochordite
Chemical formula: Mn<sup>2+</sup>Mn<sup>2+</sup><sub>2</sub>Mn<sup>2+</sup><sub>2</sub>(As<sup>5+</sup>O<sub>4</sub>)<sub>2</sub>(OH)<sub>4</sub>(H<sub>2</sub>O)<sub>4</sub>
Akrochordite is a rare, hydrated manganese arsenate, forming characteristic aggregates in the form of warts or spherulites.
Properties
- Mohs hardness
- 3.5
- Luster
- Vitreous to greasy
- Streak
- White
- Density
- 3.19
- Cleavage
- Good on {010}
- Fracture
- Uneven
- Transparency
- Translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification The key diagnostic feature of akrochordite is its unique form as small, spherical or "wart-like" aggregates. The place of origin (Långban, Sterling Hill) and co-occurrence with other manganese minerals are also important. ## Distinguishing from Similar Minerals It can be confused with other arsenates or carbonates with a similar botryoidal structure, such as allactite, sarkinite, or kutnohorite, which occur in the same localities. Certain differentiation often requires hardness analysis, reaction with acids, or advanced research methods, but the characteristic "wart-like" appearance is a strong indicator. ## Crystal Forms Akrochordite almost always occurs in the form of spherical, botryoidal, or reniform aggregates. Single, well-formed crystals are extremely rare and appear as small, tabular forms.
Geological environment
## Genesis It is a rare secondary mineral, formed in iron and manganese ore deposits that have undergone metamorphic processes. It is most commonly found in vugs and fissures within hausmannite-dolomite skarns. ## Mineral Associations Akrochordite often co-occurs with minerals such as hausmannite, baryte, brandtite, sarkinite, allactite, pyrochroite, and calcite. ## Localities The most important and historically first locality is the Långban mine in the Värmland region of Sweden, which is its type locality. The second significant occurrence is Sterling Hill in Ogdensburg, New Jersey, USA. Specimens from other locations are practically unheard of.
Rarity
Very rare
For collectors
## Quality Criteria The most highly valued specimens are those with well-formed, clearly separated spherical aggregates of an intense, reddish-brown color. Placement on a contrasting rock matrix, as well as the presence of other rare minerals, especially from Långban or Sterling Hill, adds significant value. ## Popular Localities Collector specimens come almost exclusively from two classic localities: Långban in Sweden and Sterling Hill in the USA. Swedish specimens are historically most important, while American ones can be somewhat larger.
Care and storage
## Cleaning Akrochordite specimens should be cleaned very carefully, using only a soft brush and distilled water. Ultrasonic cleaners should be avoided, as they can damage delicate aggregates. ## What to Avoid The mineral is sensitive to acids and strong chemicals. As a hydrated mineral, it is also susceptible to damage from high temperatures, which can lead to dehydration and structural degradation. Prolonged exposure to direct sunlight should be avoided. ## Storage It is recommended to store specimens in stable conditions, in separate, padded boxes, to prevent abrasion and mechanical damage. It should not be stored in contact with harder minerals.