Manganhumite

Chemical formula: Mn²⁺₇(SiO₄)₃(OH)₂

Manganhumite is a rare, manganese-rich silicate from the humite group, forming small, reddish-brown crystals with a vitreous luster.

## Characteristics Manganhumite is a mineral belonging to the humite group, in which it is the manganese (Mn²⁺) analogue of humite. It occurs as small, granular or poorly formed crystals, rarely exceeding a few millimeters. Its habit is usually massive or embedded in the host rock. It is a brittle mineral. ## Physical Properties It is characterized by a hardness of approximately 4 on the Mohs scale. The luster is vitreous to resinous. The mineral is usually translucent, and in thin fragments, it can be transparent. Its density is relatively high, approximately 3.83 g/cm³. ## Colors and Varieties The typical color of manganhumite is reddish-brown to dark brown. No named varieties are distinguished. ## History and Name The mineral's name refers to its chemical composition – the dominance of manganese – and its structural relationship to humite, another mineral from the same group. It was first described in 1927 based on samples from the Brattfors deposit in Sweden. ## Uses Manganhumite has no industrial application. Its significance is purely scientific and as a collector's item, as a rare representative of the humite group and manganese-rich metamorphic minerals.

Properties

Mohs hardness: 4
Color: Pale to deep brownish-orange
Luster: Vitreous to resinous
Streak: Yellowish brown
Density: 3.83
Cleavage: {010}
Fracture: Uneven to sub-conchoidal
Transparency: Transparent
Crystal system: Orthorhombic

Diagnostic features

## Identification Manganhumite is identified by its characteristic reddish-brown color, vitreous luster, and occurrence in manganese-rich metamorphic rocks. Small crystal size and granular form are also typical. Identification is confirmed based on its hardness (approx. 4) and relatively high density. ## Distinguishing from Similar Minerals It can be confused with other minerals from the humite group, such as clinohumite or chondrodite, as well as with garnets (e.g., spessartine). Differentiation from humite minerals often requires chemical analysis (Mg to Mn ratio). It differs from spessartine by its significantly lower hardness (spessartine has a hardness of approx. 7) and usually less well-formed crystals. ## Crystal Forms Crystals are rare and usually poorly formed, with a tabular or short prismatic habit. Most often, it occurs as grains or massive aggregates in the host rock.

Geological environment

## Genesis Manganhumite is a mineral of metamorphic origin. It forms as a result of contact or regional metamorphism of manganese ore deposits and sedimentary rocks rich in this element. It forms under conditions of relatively high temperatures. ## Mineral Associations It co-occurs with other manganese minerals, such as hausmannite, galaxite, rhodonite, tephroite, sonolite, as well as with barite, calcite, and other minerals from the humite group. ## Localities Key localities for manganhumite include the Brattfors deposit in Filipstad municipality (Sweden), which is its type locality. It is also found in the Bald Knob mines (North Carolina, USA), Wessels (Northern Cape Province, South Africa), and in Tochigi Prefecture, Japan.

Rarity

Rare

For collectors

## Quality Criteria The most prized manganhumite specimens have well-formed, even if small, crystals with an intense, reddish-brown color and good luster. Contrast with a light host rock (e.g., with calcite), which highlights the crystals, is important. Specimens from classic, historical localities, such as Brattfors, are particularly sought after. ## Popular Localities Specimens from the Wessels deposit in South Africa, which yielded specimens with relatively well-formed crystals, are considered the best for collectors. Samples from Sweden (Brattfors) also have historical significance.

Care and storage

## Cleaning Manganhumite specimens should be cleaned very carefully, using a soft brush to remove dust. If necessary, a damp cloth with distilled water can be used, and then the specimen should be dried immediately. Ultrasonic cleaners should be avoided. ## What to Avoid The mineral is sensitive to acids, which can damage it. Contact with household and laboratory chemicals should be avoided. Due to its relatively low hardness, it is susceptible to scratches. ## Storage It is recommended to store specimens in separate, padded boxes to prevent abrasion and scratches from harder minerals. It should be protected from dust and moisture.

External references

https://www.mindat.org/min-2470.html