Manganilvaite

Chemical formula: CaFe₂+Fe₃+Mn₂+(Si₂O₇)O(OH)

Manganilvaite is a rare sorosilicate of the ilvaite group, distinguished by its significant manganese content, forming black, prismatic crystals.

## Characteristics Manganilvaite is a mineral belonging to the ilvaite group, serving as its manganese analog. It forms elongated, prismatic crystals with an almost square cross-section, terminated by flat or complex faces. It also occurs as radial aggregates, granular masses, or solid masses. Its crystals are typically opaque and black in color. ## Physical Properties This mineral is characterized by a hardness of 5.5-6 on the Mohs scale and a significant density of approximately 3.99 g/cm³. It is brittle, and its fracture is uneven to conchoidal. The luster of manganilvaite is described as metallic to submetallic. ## Colors and Varieties The predominant and only observed color of manganilvaite is black. No colored or commercial varieties are distinguished. ## History and Name The mineral's name, given in 1986 by Japanese mineralogists (Takeuchi, Haga, Komatsu, Kobayashi), refers to its chemical composition – high manganese content – and its structural similarity to ilvaite. It was discovered in the Hijikuzu mine (originally named Hinokuzu) in Iwate Prefecture, Japan. ## Applications Manganilvaite has no industrial applications. It is solely an object of interest for collectors of rare minerals and scientists studying skarns and metasomatic processes.

Properties

Mohs hardness: 5.5 - 6
Luster: Metallic to submetallic
Streak: Black
Density: 3.99
Cleavage: Good on {010} and {100}
Fracture: Uneven to conchoidal
Transparency: Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Characteristic features of manganilvaite include its black color, metallic or submetallic luster, and typical shape of long, prismatic crystals. High density is also a helpful diagnostic indicator. ## Distinguishing from Similar Minerals It can be confused with ilvaite, from which it is practically impossible to distinguish without chemical analysis (manganilvaite contains >50% manganese in place of one of the iron atoms). It can also resemble black tourmaline (schorl), which, however, crystallizes in the trigonal system and often exhibits characteristic striations on prism faces, and also has a lower density. It also differs from hornblende, which has perfect cleavage. ## Crystal Forms Manganilvaite forms columnar, prismatic crystals, often with a nearly square cross-section. Crystals can occur individually or form radial aggregates. It is also found in granular and massive forms.

Geological environment

## Genesis Manganilvaite is a mineral typical of manganese skarns. It forms as a result of metasomatic processes at the contact of magmatic intrusions (e.g., granodiorites) with manganese-rich sedimentary rocks, such as rhodochrosite deposits. ## Mineral Associations It co-occurs with minerals such as rhodochrosite, bustamite, tephroite, galena, pyroxmangite, sphalerite, quartz, and garnets from the spessartine-grossular series. ## Localities The most important and best-formed specimens come from the type locality – the Hijikuzu mine in Iwate Prefecture, Japan. This mineral has also been identified in several other locations worldwide, including Broken Hill in Australia, the Ilímaussaq complex in Greenland, the Dalnegorsk mines in the Russian Far East, and in Sweden (e.g., Sjögruvan).

Rarity

Rare

For collectors

## Quality Criteria The most valued by collectors are specimens with well-formed, sharp, and undamaged crystals with a strong luster. Large, single prisms or aesthetic radial groups are particularly sought after. The value of a specimen is enhanced by its association with contrasting minerals, such as pink rhodochrosite. ## Popular Localities Undoubtedly, the most desirable and classic manganilvaite specimens come from its type locality in Japan (Hijikuzu mine). Specimens from other localities, such as Dalnegorsk in Russia, are also sometimes available on the collector's market and are valued for crystal quality.

Care and storage

## Cleaning Manganilvaite specimens should be cleaned very carefully, using a soft brush to remove dust. If necessary, distilled water can be used, followed by thorough drying of the specimen. Ultrasonic cleaners should be avoided, as they can cause cracks. ## What to Avoid This mineral is sensitive to strong acids. It should be protected from sudden temperature changes and prolonged exposure to moisture, which can initiate weathering processes. Avoid impacts and drops due to its brittleness. ## Storage It is recommended to store specimens in separate, padded boxes or display cases to prevent scratches from harder minerals. Exposure should be in stable conditions, away from direct sunlight and heat sources.

Sources

IMA Mineral List (CNMNC)